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

wrangler.jsonc

@@ -59,34 +59,8 @@
   //
   // See .dev.vars.example for a full reference of all variables.
   // ────────────────────────────────────────────────────────────────────
-
-  // ── Cloudflare D1 database (story persistence — optional) ───────────
-  // Not required for core gameplay. Uncomment and fill in your ID if needed:
-  //   wrangler d1 create infiplot-db
-  // "d1_databases": [
-  //   {
-  //     "binding": "DB",
-  //     "database_name": "infiplot-db",
-  //     "database_id": "<your-d1-database-id>"
-  //   }
-  // ],
-
-  // ── Cloudflare R2 bucket (asset storage — optional) ─────────────────
-  // Not required for core gameplay. Uncomment if needed:
-  //   wrangler r2 bucket create infiplot-assets
-  // "r2_buckets": [
-  //   {
-  //     "binding": "R2_BUCKET",
-  //     "bucket_name": "infiplot-assets"
-  //   }
-  // ],
-
-  // ── Cloudflare KV namespace (reserved for future use) ───────────────
-  // Uncomment if needed: wrangler kv namespace create KV
-  // "kv_namespaces": [
-  //   {
-  //     "binding": "KV",
-  //     "id": "<your-kv-namespace-id>"
-  //   }
-  // ]
+  //
+  // Story persistence is browser-local (IndexedDB) in the open-source build and
+  // Supabase (Postgres) in the commercial build — no Cloudflare D1/R2/KV
+  // bindings are used.
 }