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.

vitest.config.ts

@@ -47,7 +47,10 @@ export default defineConfig({
         test: {
           name: "frontend",
           environment: "jsdom",
-          include: ["src/ui/**/*.test.{ts,tsx}"],
+          include: [
+            "src/ui/**/*.test.{ts,tsx}",
+            "plugins/**/frontend/**/*.test.{ts,tsx}",
+          ],
         },
       },
       {