feat: add Studio current-frame capture

[miguel-heygen]

Problem

Closes #555. Studio users could inspect the preview, but there was no first-class way to capture the current rendered frame as an image.

What this fixes

• Adds a Capture action to the Studio header toolbar so it does not cover the video preview.
• Downloads the current composition frame as a PNG using the current player time.
• Extends the existing thumbnail route and Studio/CLI thumbnail generators with an explicit PNG format path while preserving JPEG thumbnails for existing previews.
• Adds URL/filename utility coverage plus thumbnail route coverage for PNG requests.

Root cause

Studio already had frame thumbnail generation, but the API path was JPEG-oriented and the editor UI only used it for previews. There was no current-frame capture affordance wired to the player state.

Verification

Local

• bun run --filter @hyperframes/core test src/studio-api/routes/thumbnail.test.ts
• bun run --filter @hyperframes/studio test src/utils/frameCapture.test.ts src/player/components/PlayerControls.test.ts
• bun run --filter @hyperframes/studio typecheck
• bun run --filter @hyperframes/core typecheck
• bun run --filter @hyperframes/cli typecheck
• bunx oxlint packages/cli/src/server/studioServer.ts packages/core/src/studio-api/routes/thumbnail.test.ts packages/core/src/studio-api/routes/thumbnail.ts packages/core/src/studio-api/types.ts packages/studio/src/App.tsx packages/studio/src/icons/SystemIcons.tsx packages/studio/vite.config.ts packages/studio/src/utils/frameCapture.ts packages/studio/src/utils/frameCapture.test.ts
• bunx oxfmt --check packages/cli/src/server/studioServer.ts packages/core/src/studio-api/routes/thumbnail.test.ts packages/core/src/studio-api/routes/thumbnail.ts packages/core/src/studio-api/types.ts packages/studio/src/App.tsx packages/studio/src/icons/SystemIcons.tsx packages/studio/vite.config.ts packages/studio/src/utils/frameCapture.ts packages/studio/src/utils/frameCapture.test.ts
• git diff --check

Browser

<img width="1027" height="910" alt="image" src="https://github.com/user-attachments/assets/71973af4-0279-4074-9

060-130839a2d419" />

[miguel-heygen]

Merge activity

• Apr 29, 8:48 PM UTC: @miguel-heygen merged this pull request with Graphite.