[Bug] Captions and keyboard segments overflow past trim boundary in timeline editor

[MinitJain]

Description:
When a caption or keyboard segment starts before the trim point but ends
after it, the full segment bar is shown in the timeline — extending
visually past the clip boundary.

Expected: caption/keyboard bars should stop at the trim point.
Actual: the segment bar overflows past the trim boundary.

Reproduction:

1. Open any recording with captions or keyboard segments in the editor
2. Trim the right side of the clip so the trim point cuts through a
   caption or keyboard segment
3. The segment bar extends past the trim boundary instead of stopping at it

Additional Context:

• Cap version: latest
• Operating system: macOS Sequoia 15.x
• This affects both the captions track and the keyboard track

[linear]

CAP-679

[tembo]

This is related to issue #1689 which covers caption tracks exceeding the edited video length. The core rendering happens in these files:

• apps/desktop/src/routes/editor/Timeline/CaptionsTrack.tsx - Renders caption segments
• apps/desktop/src/routes/editor/Timeline/KeyboardTrack.tsx - Renders keyboard segments
• apps/desktop/src/routes/editor/Timeline/Track.tsx - Contains SegmentRoot which calculates position/width via useSegmentTranslateX and useSegmentWidth

The segments use their raw start and end values for positioning, but these aren't being clamped to the clip boundaries. The totalDuration() function from context.ts:748-752 calculates the edited timeline length from project.timeline.segments, but the caption/keyboard segments don't currently reference this when rendering.

The fix would involve clamping segment bounds in CaptionsTrack and KeyboardTrack when iterating over segments - something like:

const clampedSegment = () => ({
  start: Math.max(segment.start, clipStart),
  end: Math.min(segment.end, clipEnd),
});

Where clipStart/clipEnd come from the current clip's trim boundaries. The ClipTrack already handles this correctly by computing relativeSegment with proper bounds (see line ~400-418).

The neighborBounds function in both tracks already uses totalDuration() for the upper bound constraint, so extending similar logic to the visual rendering should be straightforward.

[MinitJain]

Fixed in 05fdaaa - keyboard segments now pass { start: segment.start, end: Math.min(segment.end, totalDuration()) }
to SegmentRoot, consistent with how CaptionsTrack handles it.