feat(persistence): local-first story persistence (IndexedDB + Supabase skeleton)

Remove Cloudflare D1 entirely (4 API routes, lib/db/, Drizzle config/migrations,
drizzle-orm/drizzle-kit deps, wrangler D1/R2/KV bindings) and replace with
browser-local-first architecture:

Open-source build (IndexedDB, no auth):
- lib/persistence/ 5-file module: types, idb adapter (zero-dep, fault-tolerant,
  post-open invalidation retry), localStore (CRUD + sync-reserved metadata +
  slim/rebuild + retention-cap eviction with tombstone reap + sync-state
  protection + last-resort bounded fallback), sessionSlim (voice strip +
  styleRef absent-delete), cloudStore (Supabase skeleton, server-only)
- Autosave: persistence fingerprint (history.length:lastBeatCount:playerName),
  serial saveChain, failure rollback retry, replaySourceRef guard (prevents
  replayed shared stories from clobbering user saves)
- clientStoryPersistence.ts: thin facade (SaveResult discriminated union)
- Stories page: /[locale]/stories with 3-language i18n (zh-CN/en/ja)
- Homepage: book icon entry point in header

Commercial build (Supabase, skeleton only):
- Single table public.stories (JSONB + RLS 4 policies on auth.uid()=user_id)
- supabase/migrations/ DDL (idempotent)
- cloudStore.ts server-only repository, AUTH_ENABLED short-circuit
- Not wired to client this phase

Featured stories: pure fallback (buildFallbackCards + localizeCards), no D1

Includes fixes from 3 rounds of subagent code-review (tasks 16-30):
- CR1: autosave restructure, coerceOrientation, D1 comment cleanup
- CR2: fingerprint+serial+rollback+replay guard, idb post-open retry,
  enforceRetentionCap latent defense, sessionSlim absent invariant
- CR3: single-scene share guard (replaySourceRef), insert-beat fingerprint
  (beats.length), pass3 overflow double-count fix, detach gate unification

package.json

@@ -24,7 +24,6 @@
     "@fortawesome/fontawesome-free": "6.5.1",
     "@supabase/ssr": "^0.12",
     "@supabase/supabase-js": "^2.108",
-    "drizzle-orm": "^0.45.2",
     "jsonrepair": "^3.14.0",
     "jszip": "^3.10.1",
     "next": "^16.0.0",
@@ -41,7 +40,6 @@
     "@types/react-dom": "^19.0.0",
     "autoprefixer": "^10.4.20",
     "cross-env": "^10.1.0",
-    "drizzle-kit": "^0.31.10",
     "postcss": "^8.4.49",
     "sharp": "^0.33.5",
     "tailwindcss": "^3.4.15",