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-display-size.ts

@@ -0,0 +1,48 @@
+const DEFAULT_RDP_DPI = 96;
+const MAX_DEVICE_PIXEL_RATIO = 3;
+
+/**
+ * Reads a guacamoleConfig display field. The UI stores these as strings, and
+ * leaves them empty when the size should follow the browser window.
+ */
+export function readConfiguredDimension(value: unknown): number | undefined {
+  const parsed = Number(value);
+  return Number.isFinite(parsed) && parsed > 0 ? parsed : undefined;
+}
+
+export interface GuacamoleDisplaySize {
+  width: number;
+  height: number;
+  dpi?: number;
+  pixelRatio: number;
+}
+
+export function getGuacamoleDisplaySize(
+  cssWidth: number,
+  cssHeight: number,
+  protocol: string | undefined,
+  devicePixelRatio: number,
+  configuredDpi?: number,
+): GuacamoleDisplaySize {
+  const isRdp = protocol === "rdp";
+  const pixelRatio = isRdp
+    ? Math.min(
+        MAX_DEVICE_PIXEL_RATIO,
+        Math.max(1, Number.isFinite(devicePixelRatio) ? devicePixelRatio : 1),
+      )
+    : 1;
+
+  const size = {
+    width: Math.max(1, Math.round(cssWidth * pixelRatio)),
+    height: Math.max(1, Math.round(cssHeight * pixelRatio)),
+    pixelRatio,
+  };
+
+  if (!isRdp) return size;
+
+  const baseDpi =
+    configuredDpi && Number.isFinite(configuredDpi) && configuredDpi > 0
+      ? configuredDpi
+      : DEFAULT_RDP_DPI;
+  return { ...size, dpi: Math.round(baseDpi * pixelRatio) };
+}