feat(i18n): add language switcher with en/ja translations

- New client-side i18n via React Context (useI18n, tArray, I18nProvider)
- Catalog ships 21 locale stubs; only zh-CN/en/ja have reviewed translations
- Header language switcher (globe icon + short label) before settings gear
- All hardcoded Chinese UI text migrated to keys: typewriter, options,
  hints (with embedded gear icon via dangerouslySetInnerHTML), settings
  panel, footer/about, play page hints
- AI output language follows user-selected locale via trailing one-liner
  directive appended to Architect/Writer/CharacterDesigner/InsertBeat
  user messages (preserves system-prompt cacheability)
- Per-locale separator rule: zh uses middot between every glyph; en/ja
  use plain spaces
- Option value → i18n key suffix maps preserve Chinese as the underlying
  identifier so analytics unions and STYLE_MAP keys stay byte-stable

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

lib/i18n/locales/zh-HK.ts

@@ -0,0 +1,89 @@
+// Traditional Chinese (Hong Kong)
+// Auto-generated by scripts/translate-i18n.mjs
+
+export const zhHK = {
+  "layout": {
+    "metadata": {
+      "title": "InfiPlot",
+      "description": "InfiPlot"
+    }
+  },
+  "home": {
+    "examples": {
+      "male": [],
+      "female": [],
+      "x": []
+    },
+    "options": {
+      "gender": "",
+      "artStyle": "",
+      "plotStyle": "",
+      "voice": "",
+      "pacing": ""
+    },
+    "genders": {
+      "male": "",
+      "female": "",
+      "x": ""
+    },
+    "artStyles": {},
+    "plotStyles": {
+      "straightforward": "",
+      "twist": ""
+    },
+    "voiceOptions": {
+      "off": "",
+      "on": ""
+    },
+    "pacings": {
+      "fast": "",
+      "relaxed": ""
+    },
+    "stories": {},
+    "ui": {
+      "start": "",
+      "loadStory": "",
+      "settings": "",
+      "searchPlaceholder": "",
+      "noMatchingStyle": "",
+      "close": "",
+      "back": "",
+      "save": "",
+      "cancel": "",
+      "saveAndSelect": ""
+    },
+    "styleModal": {},
+    "hero": {
+      "title": "",
+      "placeholder": " ",
+      "enterHint": ""
+    },
+    "hint": {
+      "text": (params: { authEnabled?: boolean }) => {
+            const authHint = params.authEnabled ? '（測試期間，登入即可免費暢玩）' : '';
+            return `輸入想法、配置風格，點擊「開始」即可遊玩${authHint}；也可以從下方精選故事集挑一篇快速體驗 <em>InfiPlot</em>。點擊「設置」還能填入你的名字，以及你自己的文本、繪圖、識圖模型和配音 Key——全部只存在本地瀏覽器，體驗更穩定。`;
+          },
+      "closeAriaLabel": "不再顯示此提示"
+    },
+    "about": {},
+    "errors": {
+      "emptyFile": "",
+      "fileTooLarge": "",
+      "unpackFailed": "",
+      "parseFailed": "",
+      "cardNotFound": ""
+    }
+  },
+  "play": {},
+  "settings": {},
+  "auth": {},
+  "history": {},
+  "customForm": {},
+  "language": {
+    "title": "",
+    "current": "",
+    "select": ""
+  }
+} as const;
+
+export type ZhHKTranslations = typeof zhHK;