feat(ui): fenêtres View système séparées — WebviewWindow Tauri + port WindowGateway (#23)

Détache les vues dans de vraies fenêtres système Tauri (multi-écran,
fullscreen). Backend : commandes de gestion de WebviewWindow, capabilities
et composition root. Frontend : nouveau port WindowGateway et son adaptateur
window, entrée panel-only ViewWindow/ViewPanelBody, détachement câblé dans
ProjectsView. QA vert : app-tauri 63, frontend typecheck + vitest 546/546.

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

frontend/src/adapters/mock/index.ts

@@ -84,6 +84,8 @@ import type {
   TicketListQuery,
   CreateTicketInput,
   UpdateTicketInput,
+  ViewWindowClosed,
+  WindowGateway,
   WorkStateGateway,
 } from "@/ports";
 import { normalizeProjectWorkState } from "../workStateNormalization";
@@ -1086,6 +1088,51 @@ class MockRemoteGateway implements RemoteGateway {
   async connect(): Promise<void> {}
 }
 
+/**
+ * In-memory {@link WindowGateway} for tests/dev (#23). Tracks which views are
+ * "detached" in a set keyed by `panel|projectId`, and lets tests simulate the
+ * OS closing a window via {@link simulateOsClose}. `closeViewWindow` also emits
+ * the close event, mirroring the backend (a programmatic close still notifies).
+ */
+export class MockWindowGateway implements WindowGateway {
+  /** Currently-open detached windows, keyed `panel|projectId`. */
+  readonly open = new Set<string>();
+  private readonly listeners = new Set<(e: ViewWindowClosed) => void>();
+
+  private key(panel: string, projectId: string): string {
+    return `${panel}|${projectId}`;
+  }
+
+  async openViewWindow(panel: string, projectId: string): Promise<void> {
+    this.open.add(this.key(panel, projectId));
+  }
+
+  async closeViewWindow(panel: string, projectId: string): Promise<void> {
+    if (this.open.delete(this.key(panel, projectId))) {
+      this.emit({ panel, projectId });
+    }
+  }
+
+  async onViewWindowClosed(
+    handler: (event: ViewWindowClosed) => void,
+  ): Promise<Unsubscribe> {
+    this.listeners.add(handler);
+    return () => {
+      this.listeners.delete(handler);
+    };
+  }
+
+  /** Test hook: simulate the user closing the OS window (fires the event). */
+  simulateOsClose(panel: string, projectId: string): void {
+    this.open.delete(this.key(panel, projectId));
+    this.emit({ panel, projectId });
+  }
+
+  private emit(event: ViewWindowClosed): void {
+    for (const l of this.listeners) l(event);
+  }
+}
+
 /**
  * The pre-filled reference catalogue the mock serves — mirror of the backend's
  * **selectable** catalogue (§17.3/D7): only profiles drivable in structured mode
@@ -2400,6 +2447,7 @@ export function createMockGateways(): Gateways {
     workState: new MockWorkStateGateway(),
     conversation: new MockConversationGateway(),
     ticket: new MockTicketGateway(systemGateway),
+    window: new MockWindowGateway(),
   };
 }
 

frontend/src/adapters/mock/mock.test.ts

@@ -30,6 +30,7 @@ describe("createMockGateways", () => {
       "template",
       "terminal",
       "ticket",
+      "window",
       "workState",
     ]);
   });