Add QR codes to address pages with redesigned layout

- Installed qrcode npm package for QR generation
- Created reusable QRCode.svelte component
- Completely redesigned address page layout:
  - Prominent QR code display (200x200px)
  - Grid layout with QR + address info + balance stats
  - Copy address button with feedback
  - Stats grid showing transactions, UTXOs, sent, net activity
  - Enhanced UTXO table with clickable block heights
  - Better visual hierarchy and spacing
- QR code shows even if address index disabled
- White QR on dark background matching site theme
- Added proper meta descriptions for SEO

Address pages now have professional layout with scannable QR codes!

package.json

@@ -23,6 +23,7 @@
   },
   "dependencies": {
     "chart.js": "^4.4.0",
-    "leaflet": "^1.9.4"
+    "leaflet": "^1.9.4",
+    "qrcode": "^1.5.4"
   }
 }