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/SKILL.md

@@ -475,9 +475,9 @@ Refs are invalidated on navigation — run `snapshot` again after `goto`.
 ### Server
 | Command | Description |
 |---------|-------------|
-| `connect [browser] [--port N]` | Connect to real Chrome/Comet browser via CDP |
-| `disconnect` | Disconnect from real browser, return to headless mode |
-| `focus [@ref]` | Bring connected browser window to foreground (macOS) |
+| `connect` | Launch headed Chromium with Chrome extension |
+| `disconnect` | Disconnect headed browser, return to headless mode |
+| `focus [@ref]` | Bring headed browser window to foreground (macOS) |
 | `handoff [message]` | Open visible Chrome at current page for user takeover |
 | `restart` | Restart server |
 | `resume` | Re-snapshot after user takeover, return control to AI |