Replace mutable merged tracks with read-only projections

[PaulHax]

Replace mutable merged tracks with read-only projections

The multicamera track list returned a cloned Track model. The clone still had mutation methods
and notification state. A caller could change the clone without changing the stored camera tracks.

The single-camera path returned a live model. Thus, the two paths had different read and write
behavior.

Changes

• Add a data-only TrackProjection for logical-track reads.
• Give single-camera and multicamera callers the same read interface.
• Remove mutation methods, notification state, and revision references from projections.
• Add pure helpers for display type, features, interpolation, split checks, and keyframe navigation.
• Cache each projection until a source camera track or camera set changes.
• Route notes, attributes, feature attributes, keyframes, and interpolation through CameraStore
  commands.
• Remove the obsolete notification bypass from Track.merge.

An edit in any camera invalidates the related projection. This includes an edit in a camera that is
not the canonical camera.

Manual tests

Test data: download and extract classification.zip. Paths below are relative to dive-classification-test-data/.

Multicamera row edits

1. Create the dataset from
   dive-classification-test-data/classification/multicamera-linked-types/.
2. Edit a note, track attribute, detection attribute, and keyframe; then save, reload, and switch
   cameras.

Verify: The logical-track view shows the saved note, attributes, and keyframe geometry after reload.

Projection refresh from either camera

1. Create the dataset from
   dive-classification-test-data/multicamera/divergent-classification-replicas/.
2. Edit track 2 from port, then edit it from starboard.

Verify: The list and Track Details refresh after either camera track changes.

Stack

This is PR 6 of 9. Previous: centralize classification changes.
Next: make lifecycle operations classification-safe.

1. Allow devDependency imports in TypeScript spec files
2. Preserve warnings from every Desktop import file
3. Copy source metadata when creating a single-camera soft clone
4. Add hierarchical track classification
5. Centralize hierarchical classification changes
6. Current — Replace mutable merged tracks with read-only projections
7. Make track lifecycle operations classification-safe
8. Add lossless DIVE KWCOCO classification support
9. Define raw and resolved classification boundaries

This PR is stacked on hierarchical-classification-pr2-mutations.

Overall: 24 files, +808/-151. Commits: 523556b9 through 9bc865e1.