feat(builder): B5 — share + promote-to-project wizard (t-paliad-350)

Litigation Builder slice B5 (m/paliad#153 PRD §2.4 + §2.5 + §5.4 + §10).

Backend (internal/services/scenario_builder_service.go):
- ListSharedWithMe — scenarios shared read-only with the caller (the
  "Geteilt mit mir" bucket).
- PromoteScenario — transactional promote-to-project (PRD §10, no partial
  promotions). One Postgres tx: INSERT paliad.projects ('case',
  origin_scenario_id, proceeding_type_id + scenario_flags from the primary
  triplet) → creator team lead + wizard-selected colleagues → parties →
  deadlines (filed→completed, planned→pending with computed/actual date,
  skipped→none) → flip scenario to 'promoted' + promoted_project_id. The
  primary top-level proceeding + its spawned descendants form the one case
  file; additional standalone proceedings are reported via
  ProceedingsSkipped and stay in the scenario. Planned dates come from the
  injected FristenrechnerService.Calculate; court-set/undated planned
  events are skipped + counted.
- NewScenarioBuilderService gains a *FristenrechnerService dep (wired in
  cmd/server/main.go; nil in tests that don't promote).

Handlers/routes:
- GET /api/builder/scenarios/shared, POST /api/builder/scenarios/{id}/promote.

Frontend:
- builder-shares.ts — share modal (HLC user picker + current-shares list +
  revoke).
- builder-promote.ts — 3-step wizard (Bestätigen → Parteien ergänzen →
  Akte-Metadaten) → POST /promote → navigate to /projects/{id}.
- builder.ts — bucketed side panel (Aktiv / Geteilt mit mir / Als Projekt
  angelegt / Archiviert), read-only chrome (watermark + locked affordances)
  for shared/promoted scenarios, wired share + promote buttons, deep-link
  auto-load now covers shared scenarios.
- procedures.tsx — enabled buttons, bucket containers, readonly watermark slot.
- global.css — modal scaffold, share UI, promote wizard, buckets, readonly
  state. i18n.ts + i18n-keys.ts — DE+EN keys.

Tests: TestScenarioBuilderPromote (live-DB) pins the transactional cascade
+ readonly-after-promote + re-promote rejection. go build/vet/test + bun
build clean. Verified end-to-end via Playwright: Journey E (share → 2nd
user read-only watermark + locked canvas, incl. deep-link) and Journey D
(promote wizard 3 steps → project created with party → navigate → scenario
flipped to promoted).

cmd/server/main.go

@@ -256,7 +256,7 @@ func main() {
 			// Akte-mode dual-write: project-backed scenarios write through
 			// to paliad.projects.scenario_flags + paliad.deadlines via the
 			// injected project + scenarioFlags services.
-			ScenarioBuilder: services.NewScenarioBuilderService(pool, projectSvc, services.NewScenarioFlagsService(pool, projectSvc)),
+			ScenarioBuilder: services.NewScenarioBuilderService(pool, projectSvc, services.NewScenarioFlagsService(pool, projectSvc), services.NewFristenrechnerService(rules, holidays, courts)),
 		}
 
 		// t-paliad-246 Slice A — Backup Mode runner. Wired only when