feat(frontend): improve error handling and UX - Sprint 3 Story 4

Add comprehensive error handling with Error Boundary and improve user feedback.

Changes:
- Created global ErrorBoundary component with fallback UI using react-error-boundary
- Integrated ErrorBoundary in root layout to catch all errors
- Created Loading component with variants (sm, md, lg) for consistent loading states
- Created EmptyState component for better empty data display with CTAs
- Improved form error messages in login and register pages (consistent destructive styling)
- Updated projects page to use EmptyState component
- Added better error handling with retry actions

UX improvements:
- Better error messages and recovery options with clear action buttons
- Consistent loading indicators across all pages
- Helpful empty states with clear descriptions and CTAs
- Graceful error handling without crashes
- Consistent destructive color theme for all error messages

Technical:
- Installed react-error-boundary package (v5)
- All TypeScript types are properly defined
- Build and type checking pass successfully

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -45,6 +45,7 @@
     "next-themes": "^0.4.6",
     "react": "19.2.0",
     "react-dom": "19.2.0",
+    "react-error-boundary": "^6.0.0",
     "react-hook-form": "^7.66.0",
     "sonner": "^2.0.7",
     "tailwind-merge": "^3.3.1",