feat(frontend): host les fenêtres plugin et l'API publique windows.open

Ajoute la vue window host qui charge le layout plugin dans une fenêtre OS
détachée, expose react/react-dom/jsx-runtime hébergés sous
frontend/public/plugin-host pour que le runtime SDK y résolve React, et
câble services.windows.open() côté runtime plugin (loader/services/registry).

npm test -- --run src/adapters/window.test.ts src/app/ViewWindow.test.tsx
  src/plugins/runtime/loader.test.ts src/plugins/runtime/services.test.ts : 39/39
npm run typecheck : OK
npm run build : OK

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/ports/index.ts

@@ -1271,6 +1271,25 @@ export interface ViewWindowSnapshot {
   visible: boolean;
 }
 
+export interface PluginLayoutWindowOpenInput {
+  pluginId: string;
+  layoutType: string;
+  state?: JsonValue;
+}
+
+export interface PluginLayoutWindowOpenResult {
+  label: string;
+  url: string;
+  alreadyOpen: boolean;
+  providerPluginDisplayName: string;
+  layoutLabel: string;
+  surface: {
+    pluginId: string;
+    layoutType: string;
+    state: JsonValue;
+  };
+}
+
 /**
  * Detaching a View into its own OS window (ticket #23, reworked in #47).
  *
@@ -1290,6 +1309,15 @@ export interface WindowGateway {
    * main window's focused project; no project id is passed.
    */
   openViewWindow(panel: string): Promise<void>;
+  /**
+   * Opens — or focuses, if already open — a separate OS window rendering one
+   * plugin layout contribution declared in the provider plugin's
+   * `contributes.layouts`. The backend validates the provider is runtime-active
+   * and the layout type is declared before creating the window.
+   */
+  openPluginLayoutWindow(
+    input: PluginLayoutWindowOpenInput,
+  ): Promise<PluginLayoutWindowOpenResult>;
   /** Closes the detached window for `panel` if one is open. */
   closeViewWindow(panel: string): Promise<void>;
   /**