feat(ui): theme settings, stories polish, track editor restructure

- add dark/light/system theme with persisted choice + OS change listener
- restyle stories sidebar (search, item layout, border) to match captures
- move floating generate box to right column of stories, add top fade mask
- story track editor: sticky track labels aligned via flex rows, custom scrollbar with left/right zoom handles
- capture pill light mode pass, fix inline waveform progress color
- pull mcp_server hidden imports into the pyinstaller spec
- notarization doc draft

app/src/i18n/locales/zh-TW/translation.json

@@ -551,9 +551,11 @@
     "title": "故事",
     "newStory": "新增故事",
     "loading": "載入故事中…",
+    "searchPlaceholder": "搜尋故事…",
     "empty": {
       "title": "尚無故事",
-      "hint": "建立您的第一個故事以開始"
+      "hint": "建立您的第一個故事以開始",
+      "noMatches": "沒有故事符合「{{query}}」"
     },
     "row": {
       "itemCount_one": "{{count}} 項",
@@ -730,6 +732,15 @@
       "label": "語言",
       "description": "選擇 Voicebox 的顯示語言。"
     },
+    "theme": {
+      "label": "佈景主題",
+      "description": "跟隨系統外觀，或固定為淺色 / 深色模式。",
+      "options": {
+        "system": "跟隨系統",
+        "light": "淺色",
+        "dark": "深色"
+      }
+    },
     "general": {
       "docs": { "title": "閱讀文件" },
       "discord": { "title": "加入 Discord", "subtitle": "取得協助與分享聲音" },