WIP: MCAP image-annotation decoder + camera-tile overlay

[mozabes]

🔗 Related Issues

WIP. First slice of the Foxglove annotations ticket: 2D image annotations end-to-end with auto-bind by topic prefix. 3D `SceneUpdate`, sidebar overlay UX, calibration projection, and dynamic channel discovery are follow-ups.

Stacks on #7633.

📋 What changes are proposed in this pull request?

Decoder layer

• New `IMAGE_ANNOTATIONS` visualization kind and renderer-neutral primitive types in `decoders/types.ts`: `ImageAnnotationCircle`, `ImageAnnotationPoints` (points / line-strip / line-loop / line-list), `ImageAnnotationText`, normalized `RgbaColor`.
• New `FOXGLOVE_IMAGE_ANNOTATIONS_PAYLOAD` descriptor.
• New `foxglove.image-annotations` decoder. Reads via the existing protobufjs schema cache; tolerates either enum-number or enum-string `type` and either camelCase or snake_case keys.
• Registered in the Foxglove built-in decoder list.

Scene inventory

• Hardcoded NuScenes inventory gains six `image-annotation` source entries (one per camera, `/CAM_*/annotations`) plus matching sync policies. Still POC-stubbed — dynamic channel discovery from the MCAP will replace this.

Camera-tile overlay

• New `ImageAnnotationsOverlay` SVG renderer for circles, polylines, points, and texts. Computes the image's displayed rect explicitly (mirroring `ImageTexturePlane`'s fit math) and positions the SVG over that rect via a `ResizeObserver` so overlays stay locked to the letterboxed image regardless of tile size.
• New `McapCameraAnnotationOverlay` (in the MCAP adapter): subscribes to one annotation topic via `useMcapTopicStream` and renders `ImageAnnotationsOverlay`.
• `ImagePanel` exposes `onImageLoaded(width, height)` so callers can size their own overlays without coupling to the panel internals.
• `McapCameraTile` derives the annotation topic from the selected camera by prefix (`/CAM_FRONT/image_rect_compressed` → `/CAM_FRONT/annotations`) and always renders an overlay alongside the image. Settings sidebar is just the source picker.

🧪 How is this patch tested? If it is not, please explain why.

• `yarn check` clean across multimodal (lint, deps, types).
• 100/100 multimodal vitest tests pass.
• Manually verified with a NuScenes `.mcap`: bounding boxes / labels stick to the rendered image as the playhead advances and as the tile is resized.

📝 Release Notes

Is this a user-facing change?

• No.
• Yes.

What areas of FiftyOne does this PR affect?

• App
• Build
• Core
• Documentation
• Other

[coderabbitai]

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