fix(canvas): size video nodes to the video's real aspect ratio

[Luna Qiu (lunaqiu)]

Fixes #105

Problem

Dragging or pasting a video onto the canvas created the node at the generic 400×300 (4:3) default, so a 720×1280 clip rendered letterboxed with large empty bars.

uploadFileToNodeInput uploaded the file without measuring it, so naturalDimensions was absent and resolveAddNodes fell back to the video type default. The image branch directly above already measured via getImageDimensionsFromBlob; the only code that ever probed a video was a private getVideoDimensions inside CanvasToolbar.tsx.

The wrong ratio was sticky: resolveGeometryEdit preserves the current box ratio for image/video, so every later resize faithfully preserved the incorrect 4:3.

Change

• utils/io/media.ts — add getVideoDimensionsFromBlob, mirroring getImageDimensionsFromBlob (preload='metadata', revokes the object URL on both paths).
• nodeInputBuilders.ts — the video branch now measures alongside the upload and passes naturalDimensions.
• CanvasToolbar.tsx — drops its two private probes and reuses the shared helpers.

Probing is non-fatal. A codec the browser cannot decode (e.g. ProRes .mov) still yields a node at the default size; previously the rejected probe propagated through Promise.all and the toolbar path dropped the node entirely.

Not covered

Agent-created video nodes hit the same default — the aspect-ratio normalizers in apps/server/src/modules/canvas/canvas-executor.ts are all gated on nodeType === 'image'. Left out deliberately: there is no video-generation tool, so an agent can only point at a pre-existing video artifact, and correcting it server-side would need an MP4/WebM metadata parser. Existing mis-sized nodes are not corrected retroactively; re-adding the file fixes them.

Verification

• Drag and Ctrl+V a 720×1280 .mp4 → node is 400×711 instead of 400×300.
• Toolbar Upload file picker and all image paths unchanged.
• pnpm typecheck clean; pnpm lint 0 errors; web unit tests 44 passing.