WIP: screen recording via chrome.tabCapture

Work in progress for navigation-safe screen recording.

Implemented:
- tabCapture permission in manifest
- Recording handlers in extension background.ts
- Recording endpoints in relay server
- Binary WebSocket streaming for video chunks
- Protocol types for recording messages
- Executor integration

Needs:
- Offscreen document implementation (tabCapture not available in service workers)
- Connect background.ts to offscreen document via messages
- Update manifest for offscreen document

The offscreen.ts/html files are scaffolding for this next step.

extension/manifest.json

@@ -3,7 +3,7 @@
   "name": "Playwriter MCP",
   "version": "0.0.69",
   "description": "Automate your Browser using Cursor, Claude, VS Code. More capable and context efficient than Playwright MCP.",
-  "permissions": ["debugger", "tabGroups", "contextMenus", "tabs"],
+  "permissions": ["debugger", "tabGroups", "contextMenus", "tabs", "tabCapture", "offscreen"],
   "host_permissions": ["<all_urls>"],
   "background": {
     "service_worker": "background.js",