refactor: fix 9 issues from round 2 code review

Bug fixes:
- #1 /logs?level=error returned 404 — use pathname for route matching
- #2 Duplicate initialization — added 'initialized' guard flag

Should fix:
- #4 Added screenshot() to IPage interface
- #5 Graceful shutdown rejects pending requests before exit
- #6 Use process.execPath instead of 'npx tsx' for faster daemon spawn

Cleanup:
- #7 Removed duplicate 'browser' keyword in package.json
- #8 Removed unused normalizeEvaluateSource import from browser.ts
- #9 Changed dynamic import to static import in intercept.ts
- #10 Added explicit throw at end of sendCommand for clarity

61 tests pass (4 test files). Extension: 10.55KB.