feat(video): add desktop capture, editing, and browser tab recording

[dhruv-anand-aintech]

Description

• Add desktop meeting video capture for macOS display or window sources, with native playback in meeting details.
• Add an in-app trim editor with start/end sliders, playhead-based in/out points, selection preview, save, restore-original, and open-folder actions.
• Keep trimming non-destructive: the editor writes video-trimmed.mp4 and preserves the original recording. Repeated edits use the currently preferred trim, while Restore returns to the untouched source.
• Add a Manifest V3 companion extension for Chrome and Edge tab capture, including tab selection, standalone recording, stop/save, and delete controls.
• Persist the selected capture source across restarts.
• Restrict the localhost WebSocket bridge to Chromium extension origins and require its protocol token.

Related Issue

No linked issue.

Type of Change

• Bug fix
• New feature
• Documentation update
• Performance improvement
• Code refactoring
• Other

Testing

• Unit tests executed
• Manual testing performed for this PR preparation
• Full build executed
• Static JavaScript syntax checks passed for service-worker.js, offscreen.js, and popup.js
• Extension manifest JSON validation passed
• Rust source formatting and parse check passed for video_capture.rs
• Changed TSX files passed isolated TypeScript transpilation
• Git whitespace and conflict-marker checks passed

Per request, verification was limited to static checks; no build or runtime artifact checks were performed.

Documentation

• Documentation updated
• No documentation needed

Checklist

• Code follows project style
• Self-reviewed the code
• Uses existing UI primitives and Lucide icons
• Updated extension README
• Branch is up to date with devtest
• No merge conflicts

Screenshots

Not captured because verification was limited to static checks.

Additional Notes

Desktop display and exact-window capture use the macOS screencapture facility. Video trimming uses the existing FFmpeg discovery path and encodes the selected range to H.264/AAC MP4. Browser tab capture supports Chromium browsers through the unpacked extension in edge-extension.