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/rdp-credential-prompt.test.ts

@@ -0,0 +1,28 @@
+import { describe, expect, it } from "vitest";
+import { needsRdpCredentialPrompt } from "./rdp-credential-prompt";
+
+describe("needsRdpCredentialPrompt", () => {
+  it("prompts recipients when RDP has no saved authentication", () => {
+    expect(
+      needsRdpCredentialPrompt({ protocol: "rdp", rdpAuthType: "none" }),
+    ).toBe(true);
+  });
+
+  it("does not prompt when the recipient has a personal override", () => {
+    expect(
+      needsRdpCredentialPrompt({
+        protocol: "rdp",
+        rdpAuthType: "none",
+        authOverrides: {
+          rdp: { credentialId: 7, required: false, ownerAuthShared: true },
+        },
+      }),
+    ).toBe(false);
+  });
+
+  it("does not prompt for other protocols", () => {
+    expect(
+      needsRdpCredentialPrompt({ protocol: "vnc", rdpAuthType: "none" }),
+    ).toBe(false);
+  });
+});