fix(export): enable custom font rendering by serializing and writing font files to ffmpeg virtual filesystem (#1499)

[AdityaNarayanPadhi]

Summary

This PR enables custom font file uploads to render correctly in exported videos by serializing and transferring font files to the FFmpeg.wasm worker filesystem at export time (#1499).

Changes

• Lifted the useFontManager hook up from the local TextControls.tsx to useVideoEditor.ts to make custom font state globally accessible to the export pipeline.
• Updated exportVideo in ffmpeg.ts to accept the uploaded customFonts array, serialize font files to ArrayBuffer payloads, map overlay virtual file paths, and transfer them to the worker thread.
• Updated ffmpeg.worker.ts to write these binary font files to the virtual filesystem before executing the FFmpeg filter graph and added them to cleanupFiles for automatic cleanup after execution.
• Corrected buildTextFilter in text-overlay.ts to only output one valid :fontfile argument in the filter string when a custom font is used, preventing filter graph syntax errors.

Verification

• Uploading custom TTF/OTF fonts in the editor, styling text overlays with them, and exporting now successfully renders text with the custom font instead of falling back to default styling or failing exports.

[vercel]

@AdityaNarayanPadhi is attempting to deploy a commit to the magic-peach1's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

👋 Thanks for your PR, @AdityaNarayanPadhi!

Welcome to Reframe — a browser-based video editor built for everyone 🎬

What happens next

1. 🤖 Automated checks — build & TypeScript typecheck will run automatically
2. ✅ Vercel preview — a preview deployment will be created (requires maintainer authorization for fork PRs)
3. 👀 Code review — a maintainer will review your changes
4. 🚀 Merge — once approved, your PR will be merged!

Quick checklist

• PR title follows Conventional Commits (e.g. feat: add dark mode)
• Linked the issue this PR closes (e.g. Closes #123)
• Tested the changes locally (bun run dev)
• Build passes (bun run build)

Useful links

• 📖 CONTRIBUTING.md
• 🐛 Open Issues
• ⭐ Star the repo to support the project!

Happy coding! 🎉

[github-actions]

⚠️ PR Format Issues — @AdityaNarayanPadhi

Please fix the following before your PR can be reviewed:

• ⚠️ No linked issue found. Add Closes #<issue-number> to your PR description.

Push new commits after fixing — this comment will update automatically.

📖 CONTRIBUTING.md