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-websocket-url.ts

@@ -0,0 +1,31 @@
+export function buildGuacamoleWebSocketBaseUrl({
+  isDev,
+  isElectronApp,
+  isEmbeddedApp,
+  configuredServerUrl,
+  basePath,
+  location,
+}: {
+  isDev: boolean;
+  isElectronApp: boolean;
+  isEmbeddedApp: boolean;
+  configuredServerUrl?: string;
+  basePath: string;
+  location: Pick<Location, "protocol" | "host">;
+}) {
+  if (isDev) return "ws://localhost:30008";
+  if (isElectronApp) {
+    if (isEmbeddedApp || !configuredServerUrl) return "ws://127.0.0.1:30008";
+
+    const wsProtocol = configuredServerUrl.startsWith("https://")
+      ? "wss://"
+      : "ws://";
+    const wsHost = configuredServerUrl
+      .replace(/^https?:\/\//, "")
+      .replace(/\/$/, "");
+    return `${wsProtocol}${wsHost}/guacamole/websocket/`;
+  }
+
+  const wsProtocol = location.protocol === "https:" ? "wss" : "ws";
+  return `${wsProtocol}://${location.host}${basePath}/guacamole/websocket/`;
+}