refactor: architectural improvements and visual polish

- Extract custom hooks (useDocuments, useSearch, useActiveTab) from App.tsx
- Create design system primitives (Button, Card, Badge, Spinner)
- Centralize constants (tabs, fileTypes, processing stages)
- Refactor App.tsx from 329 to 180 lines for better maintainability
- Install Framer Motion for future animation enhancements
- Fix tab navigation auto-switch loop with hasAutoSwitched flag
- Replace Tailwind v4 gradient classes with inline styles for reliability
- Enhance ProcessingProgress with gradient backgrounds, spinning loader, and polished styling
- Improve AppHeader with gradient logo, better spacing, enhanced badges
- Redesign SearchInterface with larger input, better focus states, enhanced button
- Update AppNavigation with cleaner tab indicators
- Enhance PageLayout headers with gradient icons and improved typography
- Update EmptyStates with inline gradient backgrounds

All 34 tests passing, zero TypeScript errors maintained

Author: Poolchaos

package-lock.json

@@ -16,6 +16,7 @@
   "dependencies": {
     "@lancedb/lancedb": "^0.22.3",
     "@xenova/transformers": "^2.17.2",
+    "framer-motion": "^12.23.24",
     "mammoth": "^1.11.0",
     "pdfjs-dist": "^5.4.394",
     "react": "^19.2.0",