Unify browser session teardown so manual close, inactivity cleanup, and emergency shutdown all follow the same cleanup path instead of partially duplicating logic.

This changes browser_close() to delegate to cleanup_browser(), which means recording shutdown, Browserbase release, activity bookkeeping cleanup, and local socket-directory removal now happen consistently. It also updates emergency cleanup to route through cleanup_all_browsers() and explicitly clear in-memory tracking state after teardown so stale active-session, last-activity, and recording entries are not left behind on exit.

The screenshot fallback path has also been fixed. _extract_screenshot_path_from_text() now matches real absolute PNG paths, including quoted output, so browser_vision() can recover screenshots when agent-browser emits human-readable text instead of JSON.

Regression coverage was added in tests/tools/test_browser_cleanup.py for screenshot path extraction, cleanup_browser() state removal, browser_close() delegation, and emergency cleanup state clearing.

Verified with:
- python -m pytest tests/tools/test_browser_cleanup.py -q
- python -m pytest tests/tools/test_browser_console.py tests/gateway/test_send_image_file.py -q