fix(editor): keep controlled cuts contiguous and current

[lightninglu10]

Summary

Fix the controlled FreeCut timeline so cut-focused editing stays contiguous and the program monitor always represents the authoritative timeline.

• seek the playhead by clicking the timeline or a clip body, while preserving tool/control/drag behavior
• make ordinary host-mode trims ripple adjacent clips by default and keep Alt rolling trims intact
• expose the razor and split-at-playhead shortcuts directly in the split tool affordance
• clear stale skim overlays at host and playback lifecycle boundaries
• invalidate and generation-fence decoded video frames when an item is rebound to another media source
• publish the editor surface as 0.3.8

Verification

• npm run check
• npm run check:changed-health
• npm run check:edge-budgets
• focused editor/timeline/render tests: 151 passed
• full unit suite: 683 files, 4,920 tests passed
• npm run build
• npm run headless:test:portable
• npm run package:editor-surface
• npm run test:editor-surface:consumer -- --artifact artifacts/freecut-editor-surface-0.3.8.tgz (2 passed)

Notes

The consumer package remains container-sized and host-controlled. After this lands, CodePress will pin @quantfive/freecut-editor-surface@0.3.8 and run the real host frontend QA before its companion PR is merged.