feat: add intro splash screen animation on first app load

[Arsh-sudo]

Summary

Closes #1017

Adds a polished splash screen that appears on first visit before the
main app loads.

What's New

src/components/SplashScreen.tsx (new file)

• Shows Reframe logo + tagline + animated loading bar
• Fades in smoothly on mount
• Holds for 1.4s then fades out over 500ms
• Uses localStorage to show only on first visit

src/app/layout.tsx

• Import and render <SplashScreen /> inside ThemeProvider

Accessibility

• Fully respects prefers-reduced-motion — skips animation entirely
  for users with motion sensitivity
• aria-hidden="true" so screen readers skip the splash overlay

Testing

1. Clear localStorage (reframe_splash_shown)
2. Visit the app
3. Splash screen appears with logo + loading bar then fades out
4. Refresh — splash does NOT appear again
5. Set prefers-reduced-motion: reduce — splash is skipped entirely

[vercel]

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[github-actions]

✅ PR Format Check Passed — @Arsh-sudo

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.

[github-actions]

👋 Thanks for your PR, @Arsh-sudo!

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! 🎉

[magic-peach]

@Arsh-sudo This splash screen implementation is clean and well-considered — it respects prefers-reduced-motion, uses localStorage to show only on first visit, has proper aria-hidden, and the loading bar animation is a nice touch. This is the better of the two splash screen PRs.

However, CI did not run the build/lint/typecheck checks for this PR — only validate and welcome passed. I need all of build, lint, and typecheck to pass before merging.

Please make a small push to re-trigger CI:

git commit --allow-empty -m 'ci: trigger checks'
git push

Once all checks pass, this will be merged and #1024 will be closed as a duplicate.