refactor: kill CDP naming, delete chrome-launcher.ts dead code

The connectCDP() method and connectionMode: 'cdp' naming was a legacy
artifact — real Chrome was tried but failed (silently blocks
--load-extension), so the implementation already used Playwright's
bundled Chromium via launchPersistentContext(). The naming was
misleading.

Changes:
- Delete chrome-launcher.ts (361 LOC) — only import was in unreachable
  attemptReconnect() method
- Delete dead attemptReconnect() and reconnecting field
- Delete preExistingTabIds (was for protecting real Chrome tabs we
  never connect to)
- Rename connectCDP() → launchHeaded()
- Rename connectionMode: 'cdp' → 'headed' across all files
- Replace BROWSE_CDP_URL/BROWSE_CDP_PORT env vars with BROWSE_HEADED=1
- Regenerate SKILL.md files for updated command descriptions
- Move BrowserManager unit tests to browser-manager-unit.test.ts

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

browse/src/commands.ts

@@ -99,10 +99,10 @@ export const COMMAND_DESCRIPTIONS: Record<string, { category: string; descriptio
   // Handoff
   'handoff': { category: 'Server', description: 'Open visible Chrome at current page for user takeover', usage: 'handoff [message]' },
   'resume':  { category: 'Server', description: 'Re-snapshot after user takeover, return control to AI', usage: 'resume' },
-  // CDP
-  'connect': { category: 'Server', description: 'Connect to real Chrome/Comet browser via CDP', usage: 'connect [browser] [--port N]' },
-  'disconnect': { category: 'Server', description: 'Disconnect from real browser, return to headless mode' },
-  'focus':   { category: 'Server', description: 'Bring connected browser window to foreground (macOS)', usage: 'focus [@ref]' },
+  // Headed mode
+  'connect': { category: 'Server', description: 'Launch headed Chromium with Chrome extension', usage: 'connect' },
+  'disconnect': { category: 'Server', description: 'Disconnect headed browser, return to headless mode' },
+  'focus':   { category: 'Server', description: 'Bring headed browser window to foreground (macOS)', usage: 'focus [@ref]' },
 };
 
 // Load-time validation: descriptions must cover exactly the command sets