feat: Chrome/Firefox DevTools panel integration

[jamilagibson]

Context

The browser UI currently opens as a separate browser window. Integrating it as a native DevTools panel matches the UX pattern developers expect from debugging tools (React DevTools, Redux DevTools, etc.).

Acceptance criteria

• Browser UI accessible as a panel in Chrome DevTools (and optionally Firefox DevTools)
• Panel opens automatically when a connected RN app is detected
• All existing UI features (timeline, diff, tree, metrics) work within the panel constraints