feat: add toast notifications for export and copy events

[Mahi11Patel]

Description

Adds a toast notification system replacing the inline error display with non-intrusive notifications for export started, export complete, export failed/cancelled, and settings link copied.

Related Issue

Closes #99

Type of Contribution

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

Participant Info

• GitHub username: Mahi11Patel
• Contribution level (Beginner/Intermediate/Advanced): Beginner

Screen Recording

How to record: run bun run dev → open http://localhost:3000 → demonstrate the full working flow of your change, including any edge cases.

• macOS: Cmd + Shift + 5 → Record Selected Portion, or use QuickTime Player
• Windows: Win + G → Xbox Game Bar → Capture
• Linux: OBS Studio, GNOME Screenshot tool, or kazam
• Any OS: Loom (free screen recorder, great for sharing)

Recording / Loom link:

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

Toast.Notification_Mahi11Patel.mp4

• This PR is related to a valid issue
• Screen recording attached above (required for UI/feature/design changes)

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[github-actions]

👋 Thanks for your PR, @Mahi11Patel!

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

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

What happens next

1. 🤖 Automated checks — build & TypeScript typecheck will run automatically
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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 Check Passed — @Mahi11Patel

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.