feat: add fullscreen QR code for subscription connection

- New ConnectionQR page with fullscreen QR display (no modal)
- QR button in InstallationGuide header next to platform selector
- Respects hideLink setting: shows URL below QR only when visible
- i18n translations for ru, en, zh, fa

src/locales/en.json

@@ -422,7 +422,10 @@
       "notConfigured": "Connection methods are not configured yet",
       "notConfiguredUser": "Connection setup is in progress. Please check back later.",
       "notConfiguredAdmin": "No connection apps have been configured. Set them up in the Apps settings.",
-      "goToApps": "Go to Apps settings"
+      "goToApps": "Go to Apps settings",
+      "qrTitle": "Subscription QR Code",
+      "qrScanHint": "Scan to connect",
+      "qrButton": "QR Code"
     },
     "myDevices": "My Devices",
     "noDevices": "No connected devices",