perf: implement lazy loading and bundle splitting (resolves #1382)

[basantnema31]

Closes #1382

Summary

Implements a comprehensive lazy loading and bundle splitting strategy to reduce initial page load time and Time to Interactive (TTI).

Changes

src/app/page.tsx

• Replaced eager import of VideoEditor (32 KB) with next/dynamic + ssr: false
  • Shows an animated spinner while the editor chunk loads
• Replaced eager import of Footer with next/dynamic + ssr: false
  • Footer is below the fold and never needs to block first paint

src/components/VideoEditor.tsx

• Replaced eager import of ThumbnailStrip (13 KB) with next/dynamic
  • Only rendered after a file is uploaded — never needed at first paint
  • Shows an animated skeleton placeholder while loading
• Replaced eager import of OnboardingTour (11 KB) with next/dynamic
  • Only shown once on first visit — deferred completely to after hydration
• LottiePlayer was already using dynamic import() ✅

next.config.ts

• Added optimizePackageImports: ["lucide-react"] — tree-shakes unused icons
• Added webpack splitChunks config with dedicated ffmpeg and vendor cache groups for long-term browser caching

Impact

Metric	Before	After
Initial JS sent to browser	Entire editor + all components	Only shell + async chunks
VideoEditor chunk	Eagerly loaded	Deferred until after first paint
ThumbnailStrip + OnboardingTour	Always loaded	Only loaded when needed
lucide-react	Full library	Tree-shaken to used icons only
ffmpeg.wasm	Part of main bundle	Separate cached chunk

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

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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)
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Happy coding! 🎉