feat: wire remote-desktop plugin into core and rename i18n keys

Repoints core consumers (dispatcher, collab, session-sharing, tab
utils) at the plugin, adds isTabTypeAvailable gating for rdp/vnc/
telnet, widens hostCapability to accept an array, and renames the
guacamole i18n namespace to remoteDesktop.

src/ui/sidebar/AdminSettingsPanel.tsx

@@ -866,9 +866,9 @@ export function AdminSettingsPanel({
   async function handleSaveGuacamole() {
     try {
       await updateGuacamoleSettings({ enabled: guacEnabled, url: guacUrl });
-      toast.success(t("admin.guacamoleSaved"));
+      toast.success(t("admin.remoteDesktopSaved"));
     } catch {
-      toast.error(t("admin.guacamoleSaveFailed"));
+      toast.error(t("admin.remoteDesktopSaveFailed"));
     }
   }
 
@@ -879,7 +879,7 @@ export function AdminSettingsPanel({
       await updateGuacamoleSettings({ enabled: newVal, url: guacUrl });
     } catch {
       setGuacEnabled(!newVal);
-      toast.error(t("admin.guacamoleUpdateFailed"));
+      toast.error(t("admin.remoteDesktopUpdateFailed"));
     }
   }