fix(windows): fenêtres de panneau détachées suivent le projet en focus côté UI (#47)

Partie frontend. Ajoute un adaptateur focusedProject et un port dédié : la
ViewWindow détachée n'est plus liée à un project_id figé, elle s'abonne à
l'event focused-project émis par la fenêtre principale et affiche le panneau
du projet courant. ProjectsView propage le focus ; le détachement crée une
fenêtre panel-only. Couvert par les tests window/ViewWindow/focusedProject/
ProjectsView.focus.

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

frontend/src/adapters/focusedProject.ts

@@ -0,0 +1,48 @@
+/**
+ * Tauri adapter for {@link FocusedProjectGateway} (ticket #47). Bridges the
+ * main-window ⇄ detached-panel focused-project channel to the backend commands
+ * and event. 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 mirror the backend contract owned by
+ * DevBackend: `set_focused_project` / `get_focused_project` and the
+ * `focused-project://changed` event whose payload is `{ project: FocusedProject
+ * | null }`.
+ */
+
+import { invoke } from "@tauri-apps/api/core";
+import { listen } from "@tauri-apps/api/event";
+
+import type { Unsubscribe } from "@/domain";
+import type { FocusedProject, FocusedProjectGateway } from "@/ports";
+
+/** The Tauri event carrying focused-project transitions. */
+const FOCUSED_PROJECT_CHANGED = "focused-project://changed";
+
+/** Backend payload for `focused-project://changed`. */
+interface FocusedProjectChanged {
+  project: FocusedProject | null;
+}
+
+export class TauriFocusedProjectGateway implements FocusedProjectGateway {
+  async setFocusedProject(project: FocusedProject | null): Promise<void> {
+    // The backend command takes `project: Option<FocusedProjectDto>`; `null`
+    // clears the focus (no project open).
+    await invoke("set_focused_project", { project });
+  }
+
+  async getFocusedProject(): Promise<FocusedProject | null> {
+    const project = await invoke<FocusedProject | null>("get_focused_project");
+    return project ?? null;
+  }
+
+  async onFocusedProjectChanged(
+    handler: (project: FocusedProject | null) => void,
+  ): Promise<Unsubscribe> {
+    const unlisten = await listen<FocusedProjectChanged>(
+      FOCUSED_PROJECT_CHANGED,
+      (e) => handler(e.payload.project ?? null),
+    );
+    return unlisten;
+  }
+}