@remotion/browser-studio: Add project download

[JonnyBurger]

Summary

• add a typed Browser Studio capability for downloading the current virtual project
• create a safe ZIP containing project files, binary public assets, and a portable package manifest
• expose File -> Download project only when the browser capability is available
• reuse the Studio's browser download helper

Test plan

• bun run build
• bun run stylecheck
• Browser Studio, Studio, and Studio Shared package tests
• red/green verification of the Browser Studio operation wiring
• manual Browser Studio download and ZIP manifest inspection

Closes #9806

[vercel]

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Project	Deployment	Actions	Updated (UTC)
bugs	Ready	Preview, Comment	Jul 28, 2026 1:03pm
remotion	Ready	Preview, Comment	Jul 28, 2026 1:03pm

[pullfrog]

✅ No new issues found.

Reviewed changes — adds a File → Download project menu item in Browser Studio that produces a portable ZIP with resolved dependency versions, public assets, and all project source files.

• Add makeBrowserStudioProjectArchive — builds a ZIP from a VirtualProject using fflate, with path traversal protection, workspace/catalog: resolution to published versions, a default package.json fallback, and duplicate-path collision detection.
• Add downloadProject to BrowserStudioOperations — conditional operation gated on dependencyVersions, wrapped in Promise.resolve for async compatibility.
• Extract downloadBlob into packages/studio/src/helpers/download-blob.ts — moves the blob download logic out of ClientRenderQueueProcessor into a reusable helper, consumed by both the render queue and the new menu item.
• Wire File → Download project menu — appears only when getBrowserStudioOperations()?.downloadProject is available; converts the Uint8Array ZIP to a Blob via safe buffer.slice(byteOffset, byteOffset + byteLength) to handle potentially view-backed typed arrays.

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