feat: Add page loading indicator

[benperlmutter]

Summary

Adds a clear page loading indicator to provide visual feedback during navigation between pages.

Fixes #2912

Changes

New Component: RouteChangeProgress

• Top-of-page progress bar using Base blue (#0052FF)
• Animates 0% → 30% → 80% → 100% during navigation
• Only shows if navigation takes >100ms (no flash for fast pages)
• 10s timeout fallback

Accessibility Features

• ✅ Respects prefers-reduced-motion preference
• ✅ Screen reader announcements ("Loading page...", "Page loaded")
• ✅ ARIA progressbar with aria-valuenow, aria-valuemin, aria-valuemax
• ✅ High contrast mode support (forced-colors: active)
• ✅ Not focusable (tabIndex={-1})

Files Changed

• apps/web/src/components/RouteChangeProgress/index.tsx (new)
• apps/web/src/components/RouteChangeProgress/index.test.tsx (new)
• apps/web/app/AppProviders.tsx (modified)

Testing

• 14 unit tests covering render, timing, accessibility, reduced motion, and cleanup
• Manual testing recommended for visual verification

Screenshots

The progress bar appears at the top of the viewport during page navigation:

• 4px tall, Base blue (#0052FF)
• Smooth animation with glow effect
• Fades out when navigation completes

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Pull Request opened by Augment Code with guidance from the PR author

[vercel]

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[cb-heimdall]

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