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/fr.json

@@ -2,5 +2,7 @@
   "plugin.mobile-connector.err.relay_not_connected": "Relais non connecté. Renseignez le relay_url du connecteur et assurez-vous que le relais est joignable, puis réessayez.",
   "plugin.mobile-connector.err.admin_only": "Administrateur uniquement.",
   "plugin.mobile-connector.err.user_id_empty": "L'utilisateur ne doit pas être vide.",
-  "plugin.mobile-connector.err.pubkey_hex": "La clé de l'appareil doit être en hexadécimal de 32 octets."
+  "plugin.mobile-connector.err.pubkey_hex": "La clé de l'appareil doit être en hexadécimal de 32 octets.",
+  "plugin.mobile-connector.err.not_device_owner": "Vous ne pouvez révoquer que vos propres appareils.",
+  "plugin.mobile-connector.err.not_pairing_owner": "Seule la personne qui a ouvert la fenêtre d'association peut la fermer."
 }