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.

tsconfig.plugins.json

@@ -30,7 +30,8 @@
     "plugins/docker/backend/**/*.ts",
     "plugins/host-metrics/backend/**/*.ts",
     "plugins/ai/backend/**/*.ts",
-    "plugins/proxmox/backend/**/*.ts"
+    "plugins/proxmox/backend/**/*.ts",
+    "plugins/remote-desktop/backend/**/*.ts"
   ],
   "exclude": ["src/**/*.test.ts"]
 }