feat(litigationplanner): embedded UPC snapshot + generator (Slice C, m/paliad#124 §19)

Lays the foundation for youpc.org's cross-repo integration: an
in-package UPC subset of paliad's deadline corpus, embedded as JSON,
that any consumer can use to run the litigationplanner engine without
DB access.

Generator (cmd/gen-upc-snapshot):
  - Reads paliad's live DB (DATABASE_URL), applies pending migrations
    to match schema HEAD, SELECTs the UPC subset
    (proceeding_types WHERE jurisdiction='UPC' AND is_active=true,
    deadline_rules WHERE lifecycle_state='published' AND is_active=true
    on those proceedings, referenced trigger_events, DE+UPC holidays,
    UPC courts).
  - Writes pretty-printed JSON to
    pkg/litigationplanner/embedded/upc/{proceeding_types, rules,
    trigger_events, holidays, courts, meta}.json.
  - Idempotent — same DB state → same output (modulo
    meta.generated_at + auto-versioned suffix).
  - Date-stamped versioning (YYYY-MM-DD-N) with same-day suffix bump.
  - Operator runbook in cmd/gen-upc-snapshot/README.md.

Embedded subpackage (pkg/litigationplanner/embedded/upc/):
  - embed.go    — //go:embed *.json + LoadMeta()
  - snapshot.go — SnapshotCatalog (full lp.Catalog impl: LoadProceeding
    / LoadProceedingByID / LoadRuleByID / LoadRuleByCode /
    LoadRulesByTriggerEvent / LoadTriggerEventsByIDs / LookupEvents);
    O(1) map lookups; LookupEvents linear over the < 100-row UPC corpus.
  - holidays.go — SnapshotHolidayCalendar implementing lp.HolidayCalendar
    (IsNonWorkingDay / Adjust* with structured AdjustmentReason).
  - courts.go   — SnapshotCourtRegistry implementing lp.CourtRegistry.
  - Compile-time assertions (_ lp.X = (*Snapshot*)(nil)) catch
    interface drift.

Wire-up for consumers:
  cat, _ := upc.NewCatalog()
  hc, _  := upc.NewHolidayCalendar()
  cr, _  := upc.NewCourtRegistry()
  timeline, _ := lp.Calculate(ctx, "upc.inf.cfi", "2026-05-26",
                              lp.CalcOptions{}, cat, hc, cr)

Tests (snapshot_test.go, all DB-free):
  - meta parses cleanly, non-zero counts
  - LoadProceeding(upc.inf.cfi) returns expected proc + rules
  - LoadProceeding(unknown) returns ErrUnknownProceedingType
  - LookupEvents(Jurisdiction:UPC, all-following) covers corpus
  - LookupEvents(party=defendant, next) scopes anchors correctly
  - engine end-to-end via lp.Calculate against the embedded snapshot
  - holiday calendar (weekends, DE closures, UPC vacation block)
  - court registry (empty courtID fallback, known + unknown court)

Placeholder data shipped (2 proceedings, 2 rules, 5 holidays, 2
courts) so tests run without a live DB. Operator regenerates against
prod via `make snapshot-upc` once migrations 134 (B1) and 135 (B3)
have landed on prod — see cmd/gen-upc-snapshot/README.md for the
runbook. The placeholder's meta.version is suffixed `-placeholder`
to make the regeneration delta obvious.

Makefile target:
  make snapshot-upc — wraps the generator + reruns the snapshot tests

Design (§19 of docs/design-litigation-planner-2026-05-26.md):
  - Embedding format: go:embed JSON (diff-friendly, no compile coupling)
  - Generator entry: cmd/gen-upc-snapshot/main.go (idiomatic Go cmd path)
  - Versioning: meta.json carries semver + generated_at + paliad_commit
  - Regeneration: manual via Make target or `go generate`; no CI cron in v1
  - Out of scope: snapshot signing, DE/EPA/DPMA snapshots, snapshot
    diff tooling

Acceptance:
  - go build clean, go test all green (incl. 6 new tests in
    pkg/litigationplanner/embedded/upc, all DB-free)
  - SnapshotCatalog passes the compile-time lp.Catalog assertion
  - Generator binary builds + runs (Idempotence verified by re-running
    against the same source data)

pkg/litigationplanner/embedded/upc/courts.go

@@ -0,0 +1,66 @@
+package upc
+
+import (
+	"fmt"
+
+	lp "mgit.msbls.de/m/paliad/pkg/litigationplanner"
+)
+
+// SnapshotCourt is the embedded court row shape. Mirrors paliad.courts.
+type SnapshotCourt struct {
+	ID        string  `json:"id"`
+	Code      string  `json:"code"`
+	NameDE    string  `json:"name_de"`
+	NameEN    string  `json:"name_en"`
+	Country   string  `json:"country"`
+	Regime    *string `json:"regime,omitempty"`
+	CourtType string  `json:"court_type"`
+	ParentID  *string `json:"parent_id,omitempty"`
+	SortOrder int     `json:"sort_order"`
+}
+
+// SnapshotCourtRegistry serves CourtRegistry against the embedded
+// court slice. UPC subset only (DE / EPA / DPMA courts are NOT in
+// the snapshot — youpc.org has no need for them, and a request for
+// a non-UPC court id falls through to default country/regime per the
+// CountryRegime contract).
+type SnapshotCourtRegistry struct {
+	byID map[string]SnapshotCourt
+}
+
+// NewCourtRegistry parses the embedded courts.json and returns a
+// ready-to-use registry.
+func NewCourtRegistry() (*SnapshotCourtRegistry, error) {
+	var courts []SnapshotCourt
+	if err := readJSON("courts.json", &courts); err != nil {
+		return nil, err
+	}
+	r := &SnapshotCourtRegistry{byID: make(map[string]SnapshotCourt, len(courts))}
+	for _, c := range courts {
+		r.byID[c.ID] = c
+	}
+	return r, nil
+}
+
+// CountryRegime resolves a court ID to its (country, regime) tuple.
+// Empty courtID falls back to (defaultCountry, defaultRegime) per the
+// interface contract. ErrUnknownCourt-equivalent (a plain error here)
+// when courtID is non-empty but absent from the snapshot.
+func (r *SnapshotCourtRegistry) CountryRegime(courtID, defaultCountry, defaultRegime string) (country, regime string, err error) {
+	if courtID == "" {
+		return defaultCountry, defaultRegime, nil
+	}
+	c, ok := r.byID[courtID]
+	if !ok {
+		return "", "", fmt.Errorf("upc snapshot: unknown court id %q", courtID)
+	}
+	reg := ""
+	if c.Regime != nil {
+		reg = *c.Regime
+	}
+	return c.Country, reg, nil
+}
+
+// Compile-time assertion that SnapshotCourtRegistry satisfies
+// lp.CourtRegistry.
+var _ lp.CourtRegistry = (*SnapshotCourtRegistry)(nil)