feat(v1.2.0): add QR scanner with camera/upload support

- Add QRScanner component with camera and image upload
- Add QR code download button with auto-naming (SeedPGP_DATE_TIME.png)
- Split state for backup/restore (separate public/private keys and passwords)
- Improve QR generation settings (margin: 4, errorCorrection: M)
- Fix Safari camera permissions and Continuity Camera support
- Add React timing fix for Html5Qrcode initialization

Features:
- Camera scanning with live preview
- Image file upload scanning
- Automatic SEEDPGP1 validation
- User-friendly error messages
- 512x512px high-quality QR generation

package.json

@@ -9,6 +9,7 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "html5-qrcode": "^2.3.8",
     "lucide-react": "^0.462.0",
     "openpgp": "^6.3.0",
     "qrcode": "^1.5.4",