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/window.ts

@@ -0,0 +1,54 @@
+/**
+ * Tauri adapter for {@link WindowGateway} (ticket #23). Detaches a View into its
+ * own OS window by delegating to the backend's window-lifecycle commands. Like
+ * the sibling adapters, this is the only layer allowed to touch
+ * `@tauri-apps/api`; components reach it exclusively through the port.
+ *
+ * Command/event names and payloads below mirror the backend contract owned by
+ * DevBackend (build-verified). The backend exposes a single lifecycle channel
+ * `view-window://lifecycle`; this adapter narrows it to the port's close-only
+ * `onViewWindowClosed` by filtering on `kind === "closed"`.
+ */
+
+import { invoke } from "@tauri-apps/api/core";
+import { listen } from "@tauri-apps/api/event";
+
+import type { Unsubscribe } from "@/domain";
+import type { ViewWindowClosed, WindowGateway } from "@/ports";
+
+/** The single Tauri event carrying detached-window lifecycle transitions. */
+const VIEW_WINDOW_LIFECYCLE = "view-window://lifecycle";
+
+/** Backend lifecycle payload (discriminated on `kind`). */
+interface ViewWindowLifecycle {
+  kind: "opened" | "focused" | "closed";
+  panel: string;
+  projectId: string;
+  label: string;
+}
+
+export class TauriWindowGateway implements WindowGateway {
+  async openViewWindow(panel: string, projectId: string): Promise<void> {
+    // camelCase args (Tauri maps them to the command's `panel` / `project_id`).
+    await invoke("open_view_window", { panel, projectId });
+  }
+
+  async closeViewWindow(panel: string, projectId: string): Promise<void> {
+    await invoke("close_view_window", { panel, projectId });
+  }
+
+  async onViewWindowClosed(
+    handler: (event: ViewWindowClosed) => void,
+  ): Promise<Unsubscribe> {
+    // One backend channel for opened/focused/closed; the port only surfaces the
+    // close, so drop the other transitions and forward `{ panel, projectId }`.
+    const unlisten = await listen<ViewWindowLifecycle>(
+      VIEW_WINDOW_LIFECYCLE,
+      (e) => {
+        if (e.payload.kind !== "closed") return;
+        handler({ panel: e.payload.panel, projectId: e.payload.projectId });
+      },
+    );
+    return unlisten;
+  }
+}