feat(extension): 浏览器插件 P1 MVP

新建 BillNote_extension/ 工作空间（基于 vitesse-webext 骨架，Vue 3 + Vite + UnoCSS + MV3）。

P1 MVP 范围：
- popup：自动读当前 tab URL，识别 Bilibili / YouTube / 抖音 / 快手；提交 /generate_note 后轮询 /task_status；展示 markdown，复制 + 下载 .md
- options：后端地址输入与连通性测试；从 /get_all_providers + /get_models_by_provider 拉供应商/模型列表；默认画质、截图/跳转、笔记风格
- chrome.storage.local 持久化设置与最近 30 个任务，popup 重开恢复进行中任务
- markdown 里的 /static/screenshots 路径在渲染前重写为绝对地址

后端：CORS 改用 regex，新增允许 chrome-extension:// 与 moz-extension:// 源（同时保留 localhost / 127.0.0.1 / tauri.localhost）。无新增 backend endpoint。

P2-P4（content script 悬浮按钮、cookie 直通、side panel、思维导图、RAG 问答）保留 stub 文件，不在本次范围。

去掉 vitesse-webext 自带的 simple-git-hooks postinstall 配置——它会在仓库根装 pre-commit 钩子去跑 pnpm lint-staged，但仓库根没有 package.json，会破坏所有提交流。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -36,6 +36,16 @@ cd backend && ./build.sh          # Build PyInstaller backend binary
 cd BillNote_frontend && pnpm tauri build
 ```
 
+### Browser Extension (Vue 3 + vitesse-webext, MV3)
+```bash
+cd BillNote_extension
+pnpm install
+pnpm dev          # watch mode → ./extension/
+pnpm build        # production build → ./extension/
+pnpm typecheck
+```
+Load unpacked at `chrome://extensions/` → select `BillNote_extension/extension/`. Talks to the same backend at `http://localhost:8483` (configurable in the options page). CORS in `backend/main.py` already accepts `chrome-extension://` and `moz-extension://` via regex.
+
 ## Architecture
 
 **Backend** (`backend/`) — FastAPI app, entry point `main.py`:
@@ -68,6 +78,16 @@ cd BillNote_frontend && pnpm tauri build
 
 **Core Workflow**: User submits URL → task queued → download video → extract audio (FFmpeg) → transcribe (Whisper/Groq/etc) → generate notes (LLM) → frontend polls for completion → display Markdown + mind map.
 
+**Browser Extension** (`BillNote_extension/`) — Vue 3 + Vite + UnoCSS + webextension-polyfill, MV3:
+- `src/popup/Popup.vue` — main entry: detects platform from active tab URL, drives generate flow, shows progress + markdown
+- `src/options/Options.vue` — settings: backend URL, default provider/model (loaded from `/get_all_providers` + `/get_models_by_provider/{id}`), quality, screenshot/link toggles, style
+- `src/logic/api.ts` — backend API client (uses `settings.backendUrl`, unwraps `ResponseWrapper`, absolutizes `/static/screenshots/...` image paths)
+- `src/logic/storage.ts` — `chrome.storage.local`-backed Pinia-like state via `useWebExtensionStorage` for settings + last 30 tasks
+- `src/logic/platform.ts` — URL → platform detection mirroring `backend/app/validators/video_url_validator.py`
+- `src/sidepanel/`, `src/contentScripts/` — placeholders for P2/P3 (floating button, side panel mind map, RAG chat); not wired into MVP UX
+- `src/manifest.ts` — MV3 manifest, popup is default action; `host_permissions: *://*/*`
+- Polling lives client-side in popup (3 s interval while open); MV3 service worker is intentionally thin in P1
+
 ## Key Configuration
 
 - **Ports**: Backend 8483, Frontend dev 3015, Docker maps 3015→80