feat: add landing hero for first-time visitors

[jaygaikar-09]

Description

Added a responsive landing hero section for first-time visitors above the upload dropzone.

The hero introduces the product value proposition, highlights key features, and provides a prominent CTA that reuses the existing file picker flow. The hero automatically hides once a video is uploaded, preserving the current editor experience.

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Related Issue

Closes #671

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Type of Contribution

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

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Participant Info

• GitHub username: jaygaikar-09
• Contribution level (Beginner/Intermediate/Advanced): Advanced

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Screen Recording

https://drive.google.com/file/d/1vw_2R4S8YKQ3nvZv-byTIrf82ZGBActl/view?usp=sharing

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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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Summary of Changes

• Added HeroSection component
• Added responsive landing hero UI with:
  • headline
  • subheadline
  • feature pills
  • CTA button
• Hero renders only when no file is loaded
• CTA reuses the existing upload/file picker flow
• Refactored FileUpload to expose openFilePicker() via forwardRef
• Removed duplicate hidden file inputs
• Preserved existing editor/upload behavior after file selection

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[github-actions]

👋 Thanks for your PR, @jaygaikar-09!

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! 🎉

[github-actions]

✅ PR Format Check Passed — @jaygaikar-09

Basic format checks passed. A maintainer will review your code changes.

This does not mean the PR is approved — it just means the format is correct.