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/test/browser-manager-unit.test.ts

@@ -0,0 +1,17 @@
+import { describe, it, expect } from 'bun:test';
+
+// ─── BrowserManager basic unit tests ─────────────────────────────
+
+describe('BrowserManager defaults', () => {
+  it('getConnectionMode defaults to launched', async () => {
+    const { BrowserManager } = await import('../src/browser-manager');
+    const bm = new BrowserManager();
+    expect(bm.getConnectionMode()).toBe('launched');
+  });
+
+  it('getRefMap returns empty array initially', async () => {
+    const { BrowserManager } = await import('../src/browser-manager');
+    const bm = new BrowserManager();
+    expect(bm.getRefMap()).toEqual([]);
+  });
+});