Fix: Camera switching latency issue

[Manu3lde]

Improves camera device selection and video stream handling. Fixes issues when switching cameras and safely applies video track constraints.

changes

• (deviceButton.tsx)
  Stops previous stream tracks before switching, removes facingMode when deviceId is used, adds fallback to default constraints on error, listens to devicechange for dynamic updates, syncs dropdown state with active track, and handles missing labels.

• (video.tsx)
  Adds type-safe zoom constraints, checks existence of videoRef.current and srcObject before accessing capabilities, restructures cleanup to properly await track stop, and applies constraints immediately + after 500ms (instead of a fixed 2s timeout).

Closes #159