Feature: Media overlay track for images and videos on timeline

[amitayks]

Summary

A new overlay track in the timeline that lets users place images and video clips on top of their screen recording at precise time ranges, positioned and sized freely.

Key Features

• Overlay track — a second track rendered above the section track in the timeline UI, for placing, trimming, splitting, and selecting overlay media items
• Drag-and-drop import — drop image or video files onto the editor canvas to add them. Files are copied into the project folder
• Free-placement on canvas — overlay media is draggable and corner-resizable, drawn between the screen recording and PIP camera in z-order. Overflow beyond canvas is allowed (grayed in editor, clipped in render)
• Per-mode positioning — each overlay segment stores independent position/size for landscape and reel modes, following the savedLandscape/savedReel pattern
• Overlay splitting — overlays can be split at the playhead, creating two segments referencing the same source file with independent position/size
• Video overlay playback — video overlays play in sync with the timeline, with sourceStart/sourceEnd to control which part of the source plays
• Smooth transitions — overlays fade in/out at their time boundaries and interpolate position/size between split segments (0.3s)
• FFmpeg render support — overlay media composited as additional inputs with time-bounded, positioned overlay filters between the screen base and PIP camera
• Reference-counted file management — same media file can be used by multiple segments without duplication. Files are staged to .deleted/ only when all references are removed
• Overlay audio muted — video overlay audio is not included in the output

Why

Users recording screen presentations often need to show supplementary visual content — images, diagrams, or video clips — while narrating. Previously the only visual layers were the screen recording and PIP camera.

New Capabilities

• media-overlay-data — data model, normalization, validation, persistence
• media-overlay-timeline — timeline UI rendering, selection, trim, split
• media-overlay-canvas — editor canvas drag/resize, z-order, per-mode state
• media-overlay-playback — sync image/video display to timeline, fade transitions
• media-overlay-render — FFmpeg overlay filters, compositing
• media-overlay-files — import, copy, reference counting, cleanup

Related Commits

• 38af165 — feat: add media overlay track for images and videos on timeline

Fixes included in PR #3