[Feature][Video] Add "Blurred Background" padding option for Fit framing

[JavaProgswing]

Description

This PR introduces a highly requested framing mode: Fit (Blur). When resizing videos (e.g. converting a 16:9 landscape to a 9:16 vertical), the standard "Fit" mode leaves solid black bars. This new mode fills the empty space with a scaled-up, heavily blurred version of the original video.

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Related Issue

Closes #1237

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Type of Contribution

• Bug fix
• New feature
• Documentation update
• Refactor
• GSSoC contribution

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Participant Info

• GitHub username: javaprogswing
• Contribution level (Beginner/Intermediate/Advanced): Intermediate

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Screen Recording

Recording / Loom link: N/A (UI enhancement changes only)

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Checklist

• I have read the contribution guidelines
• My changes follow the project structure
• I have tested my changes in Chrome, Firefox, and Safari
• bun run lint passes (no ESLint errors)
• bunx tsc --noEmit passes (no TypeScript errors)
• New interactive elements have aria-label / accessible names
• No console.log statements left in
• This PR is related to a valid issue
• Screen recording attached above (required for UI/feature/design changes)

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[github-actions]

⚠️ PR Format Issues — @JavaProgswing

Please fix the following before your PR can be reviewed:

• ⚠️ Use a conventional PR title. Examples:
  • feat: add dark mode support
  • fix: resolve aria label missing on slider
  • docs: add deployment guide to README

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

📖 CONTRIBUTING.md

[github-actions]

👋 Thanks for your PR, @JavaProgswing!

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

🟠 GSSoC'26 PR detected — thanks for contributing under GirlScript Summer of Code 2026!

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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! 🎉

[magic-peach]

Thanks for the contribution! Another open PR (#1566: feat: Add Blurred Background padding option for Fit framing) tackles the same issue and is a bit further along (cleaner CI / no merge conflicts), so I'm consolidating there to keep review focused in one place. Closing this one — no reflection on the work itself, just avoiding split review across duplicates. Feel free to bring anything over to #1566 if it adds something that one doesn't have yet!