feat: styled offline page with app install hint, bump versions

Replace bare offline fallback with styled page matching the app's
design (glass nav, dark/light mode, wifi-off icon, retry button).
Add hint to install Android APK or PWA for offline use.

Site: 1.0.0 → 1.1.0
Android/Tauri: 0.1.0 → 0.2.0

src-tauri/tauri.conf.json

@@ -1,7 +1,7 @@
 {
   "productName": "Bocken",
   "identifier": "org.bocken.app",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "build": {
     "devUrl": "http://192.168.1.4:5173",
     "frontendDist": "https://bocken.org"