feat(t-paliad-064): migration 025 reminder redesign schema (PR-2)

Schema additions for the new digest-style reminder system:

paliad.users
- reminder_warning_offset_days INT NOT NULL DEFAULT 7, range 1..30
  Per-user customisation of how many days before each deadline the heads-up
  email fires. 7 matches the prior Monday-weekly behaviour.
- escalation_contact_id UUID NULL FK paliad.users(id) ON DELETE SET NULL
  Optional override of the escalation channel for overdue / DRINGEND mail.
  NULL means "fall back to global_admins". UI dropdown deferred to a
  follow-up task per m's 2026-04-28 decision; column ships now to avoid
  a second migration. Self-reference forbidden by CHECK constraint.

paliad.reminder_log
- slot TEXT NULL, slot_date DATE NULL — digest dedup keys.
- reminder_type CHECK widened to admit 'morning_digest' / 'evening_digest'
  alongside the legacy 'overdue' / 'tomorrow' / 'weekly' values.
- Partial UNIQUE INDEX (user_id, slot, slot_date) WHERE slot IS NOT NULL
  enforces "one digest per user per slot per local-date". Legacy rows
  with slot IS NULL are unaffected.

CLAUDE.md updated with a §Phase status note pointing to the design doc
and explaining the deferred Settings-UI dropdown for escalation_contact_id.

Migration is fully additive and idempotent (IF NOT EXISTS / DROP-then-ADD
on named constraints). Down migration reverses the schema cleanly; any
'morning_digest' / 'evening_digest' rows must be deleted before downgrading.

.claude/CLAUDE.md

@@ -66,6 +66,10 @@ Phases A–G shipped (April 2026): schema + RLS, services, Fristenrechner→DB,
 
 Phase J (this doc + roadmap rewrite + KanzlAI doc retirement notes) completed 2026-04-17 on `mai/ritchie/phase-j-roadmap-rewrite`. Infra retirement (KanzlAI Dokploy shutdown, `kanzlai` schema drop, Gitea archive) still pending m + head coordination.
 
+**Reminder system redesign (t-paliad-064)** — landed 2026-04-28 across PR-1..PR-4 on `mai/cronus/reminder-system-redesign`. Zero-overdue SLO model: per-user bundled morning/evening digests with category sections (überfällig / heute / diese Woche), DRINGEND escalation in the evening slot, and global-admin escalation framing on overdues. See `docs/design-reminder-redesign-2026-04-28.md`.
+
+> *Open follow-up:* migration 025 ships `paliad.users.escalation_contact_id` (FK to `paliad.users`, nullable, ON DELETE SET NULL). NULL means "fall back to global_admins for the escalation channel"; setting it lets a user designate a specific colleague as their escalation contact instead. The Settings → Notifications dropdown to expose this is **deferred** to a follow-up task (per m's 2026-04-28 decision). Until that ships, the column is read-only — set it via direct SQL if a user requests an explicit override.
+
 ## Worker Preferences
 
 - Use **Opus** for design/architecture decisions

internal/db/migrations/025_reminder_redesign.down.sql

@@ -0,0 +1,31 @@
+-- Roll back t-paliad-064 reminder redesign schema.
+--
+-- Drops the partial dedup index, the new columns on paliad.users and
+-- paliad.reminder_log, and restores the previous reminder_type CHECK
+-- constraint. Reversible.
+
+DROP INDEX IF EXISTS paliad.reminder_log_slot_dedup_idx;
+
+ALTER TABLE paliad.reminder_log
+    DROP CONSTRAINT IF EXISTS reminder_log_slot_check;
+
+-- Narrow the reminder_type CHECK back to the original three values. Any
+-- 'morning_digest' / 'evening_digest' rows must be deleted before this
+-- runs, or the ALTER fails.
+ALTER TABLE paliad.reminder_log
+    DROP CONSTRAINT IF EXISTS reminder_log_reminder_type_check;
+ALTER TABLE paliad.reminder_log
+    ADD CONSTRAINT reminder_log_reminder_type_check
+    CHECK (reminder_type IN ('overdue', 'tomorrow', 'weekly'));
+
+ALTER TABLE paliad.reminder_log
+    DROP COLUMN IF EXISTS slot,
+    DROP COLUMN IF EXISTS slot_date;
+
+ALTER TABLE paliad.users
+    DROP CONSTRAINT IF EXISTS users_escalation_contact_self_check,
+    DROP CONSTRAINT IF EXISTS users_reminder_warning_offset_check;
+
+ALTER TABLE paliad.users
+    DROP COLUMN IF EXISTS escalation_contact_id,
+    DROP COLUMN IF EXISTS reminder_warning_offset_days;

internal/db/migrations/025_reminder_redesign.up.sql

@@ -0,0 +1,87 @@
+-- Reminder system redesign (t-paliad-064).
+--
+-- Three things land here, in service of the new "zero-overdue SLO" model:
+--
+-- 1. paliad.users gets two new columns:
+--      * reminder_warning_offset_days — how many days before each deadline
+--        the +N-day warning email fires. Default 7 matches the prior
+--        Monday-weekly-digest behaviour. Per-user customisable on the
+--        Settings → Notifications page.
+--      * escalation_contact_id — optional pointer to another paliad.users
+--        row that should also be cc'd on overdue / DRINGEND emails. NULL
+--        means "fall back to global_admins" (the default escalation
+--        channel). The Settings UI dropdown is a follow-up task; the
+--        column ships now to avoid a second migration when wiring lands.
+--
+-- 2. paliad.reminder_log gains slot + slot_date for digest dedup. The new
+--    service writes one row per (user_id, slot, slot_date), enforced by a
+--    partial UNIQUE index. Legacy per-deadline rows (slot IS NULL) coexist
+--    and are ignored by the new dedup index — they're kept on disk for
+--    audit and a separate housekeeping migration will prune them once the
+--    new path has soaked.
+--
+-- 3. The reminder_type CHECK constraint widens to admit the two new
+--    digest values ('morning_digest', 'evening_digest'). Existing values
+--    ('overdue', 'tomorrow', 'weekly') stay valid so the legacy code path
+--    can run alongside during deploy if needed.
+--
+-- All operations are idempotent (IF NOT EXISTS on columns and index;
+-- DROP/RE-ADD on the named constraints) so a re-run is safe.
+
+-- 1) Per-user warning offset (default 7).
+ALTER TABLE paliad.users
+    ADD COLUMN IF NOT EXISTS reminder_warning_offset_days
+        INT NOT NULL DEFAULT 7;
+
+-- Range check: 1..30. A 0-day "warning" is just the same as the morning
+-- reminder, and 30+ days is so far out the email becomes noise.
+ALTER TABLE paliad.users
+    DROP CONSTRAINT IF EXISTS users_reminder_warning_offset_check;
+ALTER TABLE paliad.users
+    ADD CONSTRAINT users_reminder_warning_offset_check
+    CHECK (reminder_warning_offset_days BETWEEN 1 AND 30);
+
+-- 2) Optional escalation contact. ON DELETE SET NULL so deleting the
+--    chosen escalation user doesn't cascade-delete the source user — they
+--    just lose their override and fall back to global_admins.
+ALTER TABLE paliad.users
+    ADD COLUMN IF NOT EXISTS escalation_contact_id UUID
+        REFERENCES paliad.users(id) ON DELETE SET NULL;
+
+-- A user can't be their own escalation contact (would just bounce mail
+-- back to themselves on overdue).
+ALTER TABLE paliad.users
+    DROP CONSTRAINT IF EXISTS users_escalation_contact_self_check;
+ALTER TABLE paliad.users
+    ADD CONSTRAINT users_escalation_contact_self_check
+    CHECK (escalation_contact_id IS NULL OR escalation_contact_id <> id);
+
+-- 3) Slot-based dedup on reminder_log.
+ALTER TABLE paliad.reminder_log
+    ADD COLUMN IF NOT EXISTS slot      TEXT,
+    ADD COLUMN IF NOT EXISTS slot_date DATE;
+
+-- slot must be 'morning' | 'evening' when present (NULL = legacy row).
+ALTER TABLE paliad.reminder_log
+    DROP CONSTRAINT IF EXISTS reminder_log_slot_check;
+ALTER TABLE paliad.reminder_log
+    ADD CONSTRAINT reminder_log_slot_check
+    CHECK (slot IS NULL OR slot IN ('morning', 'evening'));
+
+-- Widen the reminder_type CHECK to admit the new digest values. Keeps the
+-- legacy values valid so coexistence during deploy is harmless.
+ALTER TABLE paliad.reminder_log
+    DROP CONSTRAINT IF EXISTS reminder_log_reminder_type_check;
+ALTER TABLE paliad.reminder_log
+    ADD CONSTRAINT reminder_log_reminder_type_check
+    CHECK (reminder_type IN (
+        'overdue', 'tomorrow', 'weekly',
+        'morning_digest', 'evening_digest'
+    ));
+
+-- Partial unique index — one digest row per (user, slot, local-date).
+-- Partial on slot IS NOT NULL so legacy rows (which have NULL slot) don't
+-- conflict with the new model.
+CREATE UNIQUE INDEX IF NOT EXISTS reminder_log_slot_dedup_idx
+    ON paliad.reminder_log (user_id, slot, slot_date)
+    WHERE slot IS NOT NULL;