feat: move remote desktop (RDP/VNC/Telnet) into a first-party plugin

Relocates guacamole backend/frontend source and tests into
plugins/remote-desktop, following the ssh-terminal/docker pattern.

plugins/remote-desktop/frontend/guacamole-session-id.ts

@@ -0,0 +1,31 @@
+import { getGuacamoleConnectionId } from "./guacamole-api";
+import type { ConnectionOrigin } from "@/lib/connection-origin";
+
+export function watchGuacamoleConnectionId(
+  connectId: string,
+  origin: ConnectionOrigin,
+  onReady: (id: string) => void,
+): () => void {
+  const controller = new AbortController();
+  let timer: ReturnType<typeof setTimeout> | undefined;
+  let attempts = 0;
+  const poll = async () => {
+    try {
+      const id = await getGuacamoleConnectionId(
+        connectId,
+        origin,
+        controller.signal,
+      );
+      if (controller.signal.aborted) return;
+      if (id) onReady(id);
+      else if (++attempts < 20) timer = setTimeout(poll, 500);
+    } catch {
+      // Session sharing discovery must not interrupt the remote display.
+    }
+  };
+  void poll();
+  return () => {
+    controller.abort();
+    clearTimeout(timer);
+  };
+}