feat(t-paliad-146): Paliadin PoC — tmux-Claude in-app AI buddy

Phase 0 of the Paliadin design (docs/design-paliadin-2026-05-07.md
§0.5). m-only laptop scope, gated behind PALIADIN_ENABLED=false on
prod. Lifts the goldi/mVoice tmux-Claude pattern (mVoice/server.py:
250-380) into a Go service: long-lived `claude` pane in a tmux
session, prompts in via `tmux send-keys -l`, responses out via a
per-turn file (/tmp/paliadin/{turn_id}.txt) the system prompt
instructs Claude to write.

What landed
-----------
- migration 058_paliadin_poc — paliad.paliadin_turns audit table
  (full prompt + response stored at PoC scope; redaction returns
  at production v1 per design §3.3). RLS: user sees own,
  global_admin sees all.

- internal/services/paliadin.go — the orchestrator. ensurePane()
  finds-or-creates the tagged tmux window, sendToPane sends the
  framed [PALIADIN:turn_id] envelope, pollForResponse reads the
  per-turn file, splitTrailer parses the [paliadin-meta] block
  Claude appends to every reply (used_tools, rows_seen,
  classifier_tag).

- internal/services/paliadin_prompt.go — the system prompt sent
  once to a fresh Claude pane. Defines the response protocol
  (Write-to-file + meta trailer), the action-chip marker syntax,
  the visibility-gate rule (paliad.can_see_project required in
  every project-scoped query), and 9 SQL recipes covering m's
  paliad data + cross-schema youpc case-law lookup.

- internal/handlers/paliadin.go — POST /api/paliadin/turn kicks
  off the work in a goroutine and returns an SSE URL; GET
  /api/paliadin/stream/{id} relays per-turn channel events
  (meta/content/end/error/ping) to EventSource. Routes register
  ONLY when PaliadinService is wired — paliadinSvc nil → no
  handlers exist, prod surface is clean.

- /admin/paliadin dashboard — global_admin-only. Shows total
  turns, last-7-days, median/p90 duration, tool-use rate (the
  load-bearing §0.5.7 metric), abandon rate, classifier
  histogram, daily sparkline, top prompts, recent turn log.
  Powered by PaliadinService.Stats() + ListRecentTurns().

- frontend: paliadin.tsx + client/paliadin.ts (chat panel with
  starter prompts, EventSource consumer, typewriter render of
  one-shot content blob, citation-chip parser, "Stop" + "New
  conversation" buttons, localStorage history); admin-paliadin
  pair (read-only stats dashboard).

- Sidebar: Paliadin entry under Übersicht (ICON_SPARKLE);
  Paliadin Monitor under Admin.

- 36 i18n keys (DE+EN), CSS for chat panel + dashboard.

- main.go: PaliadinService wires only on PALIADIN_ENABLED=true,
  with PALIADIN_TMUX_SESSION + PALIADIN_RESPONSE_DIR overrides.
  Logs visibly so the operator can confirm at boot.

- CLAUDE.md: ANTHROPIC_API_KEY row updated (PoC doesn't need it
  — Claude CLI uses m's subscription; key reserved for future
  production-v1). New rows for the three PALIADIN_* env vars.

Tests
-----
- 7 unit tests on the trailer parser, chip counter, token approx,
  and tmux-input sanitiser. All pass. The trailer parser is
  load-bearing for monitoring; an unobserved parser bug = silent
  dashboard rot.

What's NOT in v1 (stays deferred)
---------------------------------
- The Anthropic API client (production v1, gated on PoC success
  per §0.5.7).
- BYO-AI / OpenAI adapter.
- Per-user rate limiting.
- Multi-replica SSE bus.
- Mascot / avatar SVG.
- Persistent threads (history is browser localStorage only).

How to use locally
------------------
  $ export PALIADIN_ENABLED=true
  $ ./paliad
  # browse /paliadin → type a question → answers stream back
  # /admin/paliadin shows the monitoring dashboard

Migration: 058 (skips fritz's t-147 on 057). Safe on prod
because PALIADIN_ENABLED defaults to false; the table is created
but no routes touch it until the env var flips.

internal/db/migrations/058_paliadin_poc.down.sql

@@ -0,0 +1,3 @@
+-- t-paliad-146: Paliadin PoC — drop paliad.paliadin_turns.
+
+DROP TABLE IF EXISTS paliad.paliadin_turns;

internal/db/migrations/058_paliadin_poc.up.sql

@@ -0,0 +1,142 @@
+-- t-paliad-146: Paliadin PoC — paliad.paliadin_turns.
+--
+-- Design: docs/design-paliadin-2026-05-07.md §0.5.6 (PoC variant).
+--
+-- Paliadin is the in-app conversational AI assistant. Phase 0 PoC runs on
+-- m's laptop only (PALIADIN_ENABLED=false on prod default), backed by a
+-- long-lived `claude` process inside a tmux session — not the Anthropic
+-- Messages API. The PoC's load-bearing artefact is monitoring: every
+-- turn writes a row here so m can decide via /admin/paliadin whether the
+-- feature earns a production v1 build.
+--
+-- The PoC variant of this table stores the FULL prompt + response (no
+-- redaction) because m is the only user, m is m's own compliance officer,
+-- and the whole point is to read what was asked later. Production v1
+-- swaps to hash-only storage; that's a separate migration.
+--
+-- Sections:
+--   1. CREATE paliad.paliadin_turns (with RLS).
+--   2. Indexes.
+
+-- ============================================================================
+-- 1. paliad.paliadin_turns
+-- ============================================================================
+
+CREATE TABLE paliad.paliadin_turns (
+    turn_id            uuid          PRIMARY KEY DEFAULT gen_random_uuid(),
+
+    -- Who asked. FK to paliad.users (not auth.users) so deleting an auth
+    -- row leaves the audit trail intact via paliad.users.
+    user_id            uuid          NOT NULL REFERENCES paliad.users(id),
+
+    -- Browser session ID (opaque). Lets us group turns into "a single
+    -- conversation" without storing the full thread server-side.
+    session_id         text          NOT NULL,
+
+    started_at         timestamptz   NOT NULL DEFAULT now(),
+    finished_at        timestamptz,                            -- NULL until end-of-turn
+    duration_ms        int,                                    -- finished_at - started_at
+
+    -- The user's prompt, verbatim. PoC scope only — production v1 stores
+    -- a redacted hash instead. See docs/design-paliadin-2026-05-07.md §3.3.
+    user_message       text          NOT NULL,
+
+    -- Claude's response, verbatim, with the [paliadin-meta] trailer
+    -- already stripped. The trailer's parsed fields land in `used_tools`,
+    -- `rows_seen`, `chip_count`, `classifier_tag` below.
+    response           text,
+
+    -- Approximate token count (server-side word_count * 1.3). Claude Code
+    -- via tmux doesn't expose Anthropic's usage block, so this is a
+    -- coarse heuristic for the dashboard cost trend — not a billing
+    -- number.
+    response_tokens    int,
+
+    -- Tool names Claude used during this turn, parsed from the
+    -- [paliadin-meta] trailer block ("used_tools: search_my_deadlines,
+    -- lookup_court"). Empty array means Claude didn't use any tool —
+    -- the load-bearing dashboard signal: high tool-use rate justifies
+    -- the data-grounding pitch in §8.1.
+    used_tools         text[]        NOT NULL DEFAULT '{}'::text[],
+
+    -- Row counts parallel to used_tools (e.g. "rows_seen: 3, 1" → {3, 1}).
+    -- Helps spot "tool ran but returned nothing" patterns.
+    rows_seen          int[]         NOT NULL DEFAULT '{}'::int[],
+
+    -- Number of action chips Claude embedded in the response.
+    chip_count         int           NOT NULL DEFAULT 0,
+
+    -- True if the user closed the SSE stream before Claude finished.
+    abandoned          boolean       NOT NULL DEFAULT false,
+
+    -- Which paliad page m was on when he asked. Empty when invoked from
+    -- /paliadin directly.
+    page_origin        text,
+
+    -- Error code, NULL on success. Possible values:
+    --   tmux_unresponsive — couldn't write to the pane / pane died
+    --   pane_died         — tmux window closed mid-turn
+    --   user_aborted      — abandoned=true synonym, kept for query clarity
+    --   timeout           — Claude didn't write the response file in time
+    --   prompt_disabled   — PALIADIN_ENABLED=false at request time
+    error_code         text,
+
+    -- Coarse self-classification by Claude itself in the [paliadin-meta]
+    -- trailer ("data" / "concept" / "navigation" / "meta" / "other").
+    -- Drives the use-case-shape histogram on /admin/paliadin.
+    classifier_tag     text
+);
+
+-- ============================================================================
+-- 2. Indexes
+-- ============================================================================
+
+-- Per-user timeline (the "my recent paliadin turns" query). Most rows for
+-- the PoC will share user_id=m, so this index is mostly useful as a sort
+-- helper.
+CREATE INDEX paliadin_turns_user_started_idx
+    ON paliad.paliadin_turns(user_id, started_at DESC);
+
+-- Global timeline for /admin/paliadin dashboard. Keeps the dashboard
+-- queries (top-N recent turns, daily counts) on an index scan even as
+-- the table grows.
+CREATE INDEX paliadin_turns_started_idx
+    ON paliad.paliadin_turns(started_at DESC);
+
+-- Histogram queries on classifier_tag. Tiny table at PoC scale; the
+-- index pays for itself once we have weeks of data.
+CREATE INDEX paliadin_turns_classifier_idx
+    ON paliad.paliadin_turns(classifier_tag, started_at DESC)
+    WHERE classifier_tag IS NOT NULL;
+
+-- ============================================================================
+-- 3. RLS
+-- ============================================================================
+
+ALTER TABLE paliad.paliadin_turns ENABLE ROW LEVEL SECURITY;
+
+-- A user sees their own turns; global_admin sees all rows. The /admin/
+-- paliadin dashboard runs under m (global_admin) and so sees the full
+-- log. Other users would only see their own — though in PoC scope
+-- there's only m, the policy is the production-shape from day one.
+CREATE POLICY paliadin_turns_select
+    ON paliad.paliadin_turns FOR SELECT
+    USING (
+      user_id = auth.uid()
+      OR EXISTS (SELECT 1 FROM paliad.users u
+                  WHERE u.id = auth.uid() AND u.global_role = 'global_admin')
+    );
+
+-- Service-role (paliad backend) writes. Direct-auth INSERT is blocked.
+-- Paliad runs with the service role today so the policy is inert in
+-- practice; we still enable RLS so future direct-auth callers are gated.
+CREATE POLICY paliadin_turns_insert_admin_only
+    ON paliad.paliadin_turns FOR INSERT
+    WITH CHECK (false);
+
+CREATE POLICY paliadin_turns_update_admin_only
+    ON paliad.paliadin_turns FOR UPDATE
+    USING (false);
+
+COMMENT ON TABLE paliad.paliadin_turns IS
+    'Per-turn audit log for Paliadin (in-app AI). PoC variant stores full prompt + response — production v1 will swap to hash-only. Powers /admin/paliadin dashboard. Design: docs/design-paliadin-2026-05-07.md §0.5.6.';