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-file-drop.test.ts

@@ -0,0 +1,25 @@
+import { describe, expect, it } from "vitest";
+import {
+  canUploadToRdpDrive,
+  getFileDropDisposition,
+  hasDraggedFiles,
+} from "./guacamole-file-drop.ts";
+
+describe("Guacamole file drop", () => {
+  it("recognizes external file drags", () => {
+    expect(hasDraggedFiles(["Files"])).toBe(true);
+    expect(hasDraggedFiles(["text/plain"])).toBe(false);
+  });
+
+  it("rejects files when upload is unavailable instead of ignoring them", () => {
+    expect(getFileDropDisposition(["Files"], 1, false)).toBe("reject");
+    expect(getFileDropDisposition(["Files"], 1, true)).toBe("upload");
+  });
+
+  it("accepts an enabled RDP drive before a filesystem object is advertised", () => {
+    expect(canUploadToRdpDrive(true, true, false)).toBe(true);
+    expect(canUploadToRdpDrive(true, false, true)).toBe(true);
+    expect(canUploadToRdpDrive(true, false, false)).toBe(false);
+    expect(canUploadToRdpDrive(false, true, true)).toBe(false);
+  });
+});