mobile-connector: merge pairing+devices into one self-service Mobile App page

The two admin-only console pages become a single "Mobile App" page
visible to every logged-in user: connection status (with the last
connection error for troubleshooting), the device list (admin sees all,
others only their own), a pairing dialog with the QR, and — admin-only —
a settings dialog hosting the plugin config, including a relay picker
(official grayed out, test, custom URL). The generic plugin-detail
config form defers to it via the new Plugin::config_in_detail_page flag.

Pairing is now self-service: any user opens a window and the device
auto-binds to them; revocation is admin-for-anyone, owner-for-self;
(re)binding to another user stays admin-only. Binding-managed plugins
(manages_own_access) now expose their non-admin pages to all users and
self-scope per caller (web_pages_for). The relay client records the
error that ends a WS session and clears it on reconnect.

crates/plugin-mobile-connector/i18n/it.json

@@ -2,5 +2,7 @@
   "plugin.mobile-connector.err.relay_not_connected": "Relay non connesso. Imposta il relay_url del connettore e assicurati che il relay sia raggiungibile, poi riprova.",
   "plugin.mobile-connector.err.admin_only": "Solo amministratore.",
   "plugin.mobile-connector.err.user_id_empty": "L'utente non può essere vuoto.",
-  "plugin.mobile-connector.err.pubkey_hex": "La chiave del dispositivo deve essere esadecimale di 32 byte."
+  "plugin.mobile-connector.err.pubkey_hex": "La chiave del dispositivo deve essere esadecimale di 32 byte.",
+  "plugin.mobile-connector.err.not_device_owner": "Puoi revocare solo i tuoi dispositivi.",
+  "plugin.mobile-connector.err.not_pairing_owner": "Solo chi ha aperto la finestra di associazione può chiuderla."
 }