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

src/components/QrDisplay.tsx

@@ -1,4 +1,5 @@
 import { useEffect, useState } from 'react';
+import { Download } from 'lucide-react';
 import QRCode from 'qrcode';
 
 interface QrDisplayProps {
@@ -11,21 +12,61 @@ export const QrDisplay: React.FC<QrDisplayProps> = ({ value }) => {
     useEffect(() => {
         if (value) {
             QRCode.toDataURL(value, {
-                errorCorrectionLevel: 'Q',
+                errorCorrectionLevel: 'M',
                 type: 'image/png',
                 width: 512,
-                margin: 2,
+                margin: 4,
+                color: {
+                    dark: '#000000',
+                    light: '#FFFFFF'
+                }
             })
                 .then(setDataUrl)
                 .catch(console.error);
         }
     }, [value]);
 
+    const handleDownload = () => {
+        if (!dataUrl) return;
+
+        // Generate filename: SeedPGP_YYYY-MM-DD_HHMMSS.png
+        const now = new Date();
+        const date = now.toISOString().split('T')[0]; // YYYY-MM-DD
+        const time = now.toTimeString().split(' ')[0].replace(/:/g, ''); // HHMMSS
+        const filename = `SeedPGP_${date}_${time}.png`;
+
+        // Create download link
+        const link = document.createElement('a');
+        link.href = dataUrl;
+        link.download = filename;
+        document.body.appendChild(link);
+        link.click();
+        document.body.removeChild(link);
+    };
+
     if (!dataUrl) return null;
 
     return (
-        <div className="flex items-center justify-center p-4 bg-white rounded-xl border-2 border-slate-200">
-            <img src={dataUrl} alt="SeedPGP QR Code" className="w-64 h-64" />
+        <div className="flex flex-col items-center gap-4">
+            <div className="flex items-center justify-center p-4 bg-white rounded-xl border-2 border-slate-200">
+                <img
+                    src={dataUrl}
+                    alt="SeedPGP QR Code"
+                    className="w-80 h-80"
+                />
+            </div>
+
+            <button
+                onClick={handleDownload}
+                className="inline-flex items-center gap-2 px-4 py-2.5 bg-gradient-to-r from-green-600 to-green-700 text-white rounded-lg font-semibold hover:from-green-700 hover:to-green-800 transition-all shadow-lg hover:shadow-xl"
+            >
+                <Download size={18} />
+                Download QR Code
+            </button>
+
+            <p className="text-xs text-slate-500 text-center max-w-sm">
+                Downloads as: SeedPGP_2026-01-28_231645.png
+            </p>
         </div>
     );
 };