Add timeline track and clip authoring

[shaiananvari8]

Closes #10.

Summary

• Adds a compact timeline authoring toolbar for choosing a track, choosing a clip type, creating typed tracks, and creating clips on the selected track.
• Adds store actions for track selection, track category assignment, typed clip creation, segment moving, and drag lifecycle state.
• Keeps clips type-compatible with their destination track, avoids clip overlap on creation and moves, snaps movement to timeline steps, clamps negative starts to zero, and preserves legacy mixed-track horizontal movement.
• Adds focused coverage for the authoring helper logic that powers overlap checks, placement, category mapping, and track hit testing.

Validation

• npx --yes bun run --cwd packages/clap build
• npx --yes bun test packages/timeline/src/utils/timelineAuthoring.test.ts
• npx --yes bun run --cwd packages/timeline build:declaration
• npx --yes bun run --cwd packages/timeline build
• git diff --check
• Browser smoke test against the timeline Vite demo: toolbar rendered, + Track and + Clip controls were unique/clickable, a new track appeared, and no console warnings/errors were reported.

[MyTH-zyxeon]

Review-assist pass for #10 / PR #145.

I am not claiming this bounty here and I am not asking maintainers to prefer a specific submitter. Since this is a newer #10 attempt with no visible PR comments yet, I did a static acceptance pass against the issue requirements and the existing open PR queue.

What looks strong:

• The PR keeps the scope focused on timeline-native authoring: track creation, explicit track type selection, clip creation, horizontal drag, and same-type cross-track movement.
• It adds a dedicated authoring helper module plus helper tests for overlap detection, next available clip start, category-to-output mapping, and vertical track picking.
• It avoids content/entity editor work, which matches the issue's stated boundary.

Acceptance risks I would check before marking #10 complete:

1. The new test file uses bun:test, but packages/timeline/package.json currently exposes build/dev/serve scripts and no package-level test script. If the branch is claiming regression coverage, please wire the helper tests into the package/root validation path or document the exact command maintainers should run.
2. TimelineAuthoringToolbar is absolutely positioned at the top-left of ClapTimeline. It should be checked against the existing timeline camera/scale controls and the first track row so the toolbar does not hide the controls or make the first row hard to interact with.
3. Cross-track drag uses event.point.y plus getTrackAtPointY() with a top-origin negative-Y track model. Please verify this under timeline scroll/zoom/camera offset, not only at the default viewport, because a coordinate-space mismatch would make drops land on the wrong track.
4. TIMELINE_AUTHORING_CATEGORIES exposes only VIDEO, IMAGE, DIALOGUE, SOUND, MUSIC, ACTION, CAMERA, and GENERIC even though outputTypeForCategory() handles more categories. If this is intentional for MVP, it is worth documenting; otherwise the dropdown may not truly cover all supported track/clip types.
5. Rejected drag moves return false without surfacing user feedback. That may be fine, but acceptance should include a manual check that incompatible-track or overlap rejection feels deliberate rather than broken.

Suggested merge bar:

• bun run --cwd packages/timeline build or equivalent package build passes.
• A test command including the new helper tests is available and passing.
• Manual demo covers: create typed track, create clip at cursor, drag horizontally with clamping, reject overlap if policy is no-overlap, reject incompatible cross-track move, and successfully move to a compatible track.
• Maintainers pick whether Add timeline track and clip authoring #145 supersedes, complements, or borrows from feat: Add timeline track and clip creation functionality (Issue #10) #134/feat: Add timeline track and clip creation (Issue #10) #136/feat(timeline): create typed tracks and clips directly from editor(Issue #10) #139/feat(timeline): add track/clip management with drag-and-drop #140 so the bounty queue has one canonical landing path.

This should help keep the new PR reviewable without encouraging another duplicate implementation.

[catcherintheroad-hub]

Fresh local validation pass for #10 / PR #145.

Environment:

• macOS/aarch64 local checkout
• bun 1.3.11
• node v22.22.2 via PATH=/opt/homebrew/opt/node@22/bin:$PATH
• PR head: ff19518

Result:

PATH=/opt/homebrew/opt/node@22/bin:$PATH bun test packages/timeline/src/utils/timelineAuthoring.test.ts

Passed: 6 tests / 18 assertions.

PATH=/opt/homebrew/opt/node@22/bin:$PATH bun run --cwd packages/timeline build:declaration
PATH=/opt/homebrew/opt/node@22/bin:$PATH bun run --cwd packages/timeline build

Both currently stop at the same TypeScript resolution error:

src/components/controls/types.ts(1,48): error TS2307: Cannot find module 'three-stdlib' or its corresponding type declarations.

That file is unchanged between main and this PR, so this looks like a pre-existing timeline package dependency/build-environment issue rather than a #145 authoring regression.

Acceptance read after the focused test pass:

• Track creation: covered by toolbar + store helper.
• Track type dropdown: covered by TimelineAuthoringToolbar.
• Clip creation based on track type: covered by createClipOnTrack and category/output mapping helper tests.
• Horizontal drag/cross-track move path: store surface is present; the helper tests cover placement/category/track hit helpers, while a browser/manual pass would still be useful before closing.
• Scope boundary: entity/content editing remains out of scope, matching Timeline - Create new Tracks and Clips #10.

Suggested next step before close: resolve or document the three-stdlib package resolution issue so packages/timeline declaration/build checks can run cleanly, then do one browser smoke pass for toolbar track creation, typed clip creation, horizontal drag persistence, and same-type-only cross-track movement.

[catcherintheroad-hub]

Small follow-up: I opened #146 as a separate build unblocker for the three-stdlib resolution issue noted above.

#146

It only declares three-stdlib as a direct @aitube/timeline dependency and does not claim this bounty. With that dependency present, the same local packages/timeline build command passed for me.