feat(windows): persistance et restauration des fenêtres au redémarrage (#40)

Persiste l'état des fenêtres (layout/position) et le restaure au
relancement de l'application. Découpage hexagonal :
- domaine : modèle et port d'état des fenêtres (layout, ports)
- application : use cases de persistance/restauration
- infrastructure : store window_state (adapter de persistance)
- présentation : câblage app-tauri (state, commands, lib)
Couvert par des tests ciblés domaine/application/infrastructure.

Depend de #39 (fermeture des fenêtres auxiliaires).

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

crates/infrastructure/tests/window_state_store.rs

@@ -0,0 +1,60 @@
+//! Integration tests for [`FsWindowStateStore`] against a real temp directory.
+
+use std::path::PathBuf;
+use std::sync::Arc;
+
+use domain::layout::{PersistedWindowKind, PersistedWindowState, WindowStateSnapshot};
+use domain::ports::{FileSystem, WindowStateStore};
+use infrastructure::{FsWindowStateStore, LocalFileSystem};
+use uuid::Uuid;
+
+struct TempDir(PathBuf);
+
+impl TempDir {
+    fn new() -> Self {
+        let path = std::env::temp_dir().join(format!("idea-window-store-{}", Uuid::new_v4()));
+        std::fs::create_dir_all(&path).unwrap();
+        Self(path)
+    }
+
+    fn app_data_dir(&self) -> String {
+        self.0.to_string_lossy().into_owned()
+    }
+}
+
+impl Drop for TempDir {
+    fn drop(&mut self) {
+        let _ = std::fs::remove_dir_all(&self.0);
+    }
+}
+
+#[tokio::test]
+async fn window_state_save_then_load_roundtrips() {
+    let tmp = TempDir::new();
+    let fs: Arc<dyn FileSystem> = Arc::new(LocalFileSystem::new());
+    let store = FsWindowStateStore::new(fs, tmp.app_data_dir());
+
+    assert_eq!(
+        store.load_window_state().await.unwrap(),
+        WindowStateSnapshot::default()
+    );
+
+    let snapshot = WindowStateSnapshot::new(vec![PersistedWindowState {
+        label: "main".to_owned(),
+        kind: PersistedWindowKind::Main,
+        panel: None,
+        project_id: None,
+        url: None,
+        visible: true,
+        maximized: true,
+        fullscreen: false,
+        outer_position: None,
+        outer_size: None,
+        monitor: None,
+        last_focused_at: None,
+    }]);
+
+    store.save_window_state(&snapshot).await.unwrap();
+    assert_eq!(store.load_window_state().await.unwrap(), snapshot);
+    assert!(tmp.0.join("windows.json").exists());
+}