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

lib/i18n/locales/en.ts

@@ -112,6 +112,7 @@ export const en = {
       start: "Start",
       loadStory: "Load Story",
       settings: "Settings",
+      myStories: "My Stories",
       searchPlaceholder: "Search styles…",
       noMatchingStyle: "No matching styles",
       close: "Close",
@@ -388,6 +389,22 @@ Dreamy watercolor style with soft tones and nostalgic atmosphere
     current: "Current Language",
     select: "Select Language",
   },
+
+  // ========== Stories Page (app/[locale]/stories/page.tsx) ==========
+  stories: {
+    title: "M y · S t o r i e s",
+    loading: "L o a d i n g",
+    emptyTitle: "No saved stories yet",
+    emptyBack: "Go back home to start a new story",
+    scenes: "{count} scenes",
+    deleteLabel: "Delete",
+    deleteConfirm: "Delete this story? This action cannot be undone.",
+    deleteFailed: "Delete failed. Please try again later.",
+    today: "Today",
+    yesterday: "Yesterday",
+    daysAgo: "{days} days ago",
+    storiesCount: "{count} stories",
+  },
 } as const;
 
 export type EnTranslations = typeof en;

lib/i18n/locales/ja.ts

@@ -123,6 +123,7 @@ export const ja = {
       start: "スタート",
       loadStory: "シナリオ読み込み",
       settings: "設定",
+      myStories: "マイストーリー",
       searchPlaceholder: "スタイルを検索…",
       noMatchingStyle: "一致するスタイルがありません",
       close: "閉じる",
@@ -428,6 +429,22 @@ export const ja = {
     current: "現在の言語",
     select: "言語の選択",
   },
+
+  // ========== Stories Page (app/[locale]/stories/page.tsx) ==========
+  stories: {
+    title: "マ イ ス ト ー リ ー",
+    loading: "読 み 込 み 中",
+    emptyTitle: "保存されたストーリーはまだありません",
+    emptyBack: "ホームに戻って新しいストーリーを始める",
+    scenes: "{count}シーン",
+    deleteLabel: "削除",
+    deleteConfirm: "このストーリーを削除しますか？この操作は元に戻せません。",
+    deleteFailed: "削除に失敗しました。後でもう一度お試しください。",
+    today: "今日",
+    yesterday: "昨日",
+    daysAgo: "{days}日前",
+    storiesCount: "{count}件",
+  },
 } as const;
 
 export type JaTranslations = typeof ja;

lib/i18n/locales/zh-CN.ts

@@ -123,6 +123,7 @@ export const zhCN = {
       start: "开始",
       loadStory: "载入剧情",
       settings: "设置",
+      myStories: "我的剧情",
       searchPlaceholder: "搜索风格…",
       noMatchingStyle: "没有匹配的风格",
       close: "关闭",
@@ -428,6 +429,22 @@ export const zhCN = {
     current: "当前语言",
     select: "选择语言",
   },
+
+  // ========== Stories Page (app/[locale]/stories/page.tsx) ==========
+  stories: {
+    title: "我 · 的 · 剧 · 情",
+    loading: "载 · 入 · 中",
+    emptyTitle: "还没有保存的剧情",
+    emptyBack: "回到首页开始新的故事",
+    scenes: "{count} 幕",
+    deleteLabel: "删除",
+    deleteConfirm: "确认删除这个剧情？此操作无法撤销。",
+    deleteFailed: "删除失败，请稍后重试",
+    today: "今天",
+    yesterday: "昨天",
+    daysAgo: "{days} 天前",
+    storiesCount: "{count} 个剧情",
+  },
 } as const;
 
 export type ZhCNTranslations = typeof zhCN;