feat: add data-testid attributes to key UI elements for automated testing

[aditya226-sharma]

Summary

Adds data-testid attributes to key UI elements across the component tree to prepare the codebase for automated testing with Playwright or React Testing Library.

Changes

Element	data-testid value	File
File upload zone	file-upload-zone	FileUpload.tsx
Export button	export-button	VideoEditor.tsx
Progress bar	export-progress	ExportOverlay.tsx
Download button	download-button	DownloadResult.tsx
Reset button	reset-button	DownloadResult.tsx
Quality slider	quality-slider	ExportSettings.tsx
Speed slider	speed-slider	AudioSpeedControl.tsx

Acceptance Criteria

• All listed elements have data-testid attributes
• No visual or functional changes

Closes #56

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GSSoC'26 contribution

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[github-actions]

👋 Thanks for your PR, @aditya226-sharma!

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
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Happy coding! 🎉

[aditya226-sharma]

@magic-peach Gentle ping — adds data-testid attributes for testing. Ready for review!

[github-actions]

👋 This PR has been inactive for 21 days. It will be automatically closed in 14 days if there's no further activity.

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