fix(view-windows): réconcilier l'état des fenêtres détachées au boot (#50)

Branche le consommateur frontend sur la commande backend
`list_open_view_windows` : le port window expose la liste des fenêtres
de panneaux détachées réellement ouvertes côté OS, l'adaptateur Tauri
(et son double mock) l'implémente, et `ProjectsView` réconcilie le
placement des vues au démarrage à partir de ce snapshot au lieu de
supposer un état. Couvre `viewPlacement` et la réconciliation par des
tests dédiés.

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

frontend/src/features/projects/ProjectsView.tsx

@@ -61,6 +61,7 @@ import {
   isDockedTo,
   panelsDockedTo,
   placementOf,
+  reconcileDetachedWindows,
   type PanelId,
   type ViewPlacement,
   type ViewPlacements,
@@ -281,6 +282,31 @@ export function ProjectsView() {
     };
   }, [windowGateway]);
 
+  // On mount, reconcile `placements` with detached windows already open at the
+  // OS level (#50): a panel-only window restored by the OS before the main
+  // window mounted is unknown to `placements`, so the Panneaux menu would wrongly
+  // show it "Fermé". Enumerate them once and mark each as "detached" — but only
+  // best-effort and without clobbering more specific state: skip non-visible
+  // snapshots, skip `projects`/unknown panels, and never overwrite a placement
+  // the user (or a UI restore) already set to something other than "closed". A
+  // failed enumeration leaves `placements` untouched (no ghost slots). Independent
+  // of `active`: a panel-only window can be open with no active project.
+  useEffect(() => {
+    let cancelled = false;
+    void windowGateway
+      .listOpenViewWindows()
+      .then((snapshots) => {
+        if (cancelled) return;
+        setPlacements((prev) => reconcileDetachedWindows(prev, snapshots));
+      })
+      .catch(() => {
+        /* best-effort only: no reconciliation on failure */
+      });
+    return () => {
+      cancelled = true;
+    };
+  }, [windowGateway]);
+
   // Opening a conversation viewer takes over the main area — dismiss floating
   // windows so they don't obscure the viewer (LS7). Docked views stay beside it.
   function openConversation(conversationId: string) {