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.test.ts

@@ -0,0 +1,44 @@
+import { afterEach, beforeEach, expect, it, vi } from "vitest";
+const fetchId = vi.hoisted(() => vi.fn());
+vi.mock("./guacamole-api", () => ({ getGuacamoleConnectionId: fetchId }));
+import { watchGuacamoleConnectionId } from "./guacamole-session-id";
+beforeEach(() => {
+  vi.useFakeTimers();
+  fetchId.mockReset();
+});
+afterEach(() => vi.useRealTimers());
+it("discovers the sharing ID after handshake without changing the connection origin", async () => {
+  fetchId.mockResolvedValueOnce(null).mockResolvedValueOnce("guacd-id");
+  const ready = vi.fn();
+  const stop = watchGuacamoleConnectionId("connect-id", "remote", ready);
+  await vi.advanceTimersByTimeAsync(500);
+  expect(fetchId).toHaveBeenLastCalledWith(
+    "connect-id",
+    "remote",
+    expect.any(AbortSignal),
+  );
+  expect(ready).toHaveBeenCalledExactlyOnceWith("guacd-id");
+  stop();
+});
+it("ignores a late response after disconnect or replacement", async () => {
+  let resolve!: (id: string) => void;
+  fetchId.mockReturnValue(
+    new Promise<string>((done) => {
+      resolve = done;
+    }),
+  );
+  const ready = vi.fn();
+  const stop = watchGuacamoleConnectionId("old", "local", ready);
+  stop();
+  resolve("old-guacd-id");
+  await vi.advanceTimersByTimeAsync(1000);
+  expect(ready).not.toHaveBeenCalled();
+  expect(fetchId.mock.calls[0][2].aborted).toBe(true);
+});
+it("bounds discovery when the session never opens", async () => {
+  fetchId.mockResolvedValue(null);
+  const stop = watchGuacamoleConnectionId("missing", "local", vi.fn());
+  await vi.advanceTimersByTimeAsync(30000);
+  expect(fetchId).toHaveBeenCalledTimes(20);
+  stop();
+});