feat(ui): Implement Dynamic Color system and M3 Forms (Stage 2)

- Integrated @material/material-color-utilities for HCT-based color generation
- Implemented M3 Filled Text Field with floating labels and state layers
- Added Seed Color picker and palette preview to Settings
- Updated Login page with new M3 components
- Enhanced ThemeProvider with system preference listeners

Refs #3
Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -11,6 +11,7 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "@material/material-color-utilities": "^0.4.0",
     "axios": "^1.15.0",
     "lucide-react": "^1.8.0",
     "react": "^19.2.4",