feat: add desktop sidebar collapse to icon-only mode (refs #176)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/core/store/app.ts

@@ -4,21 +4,31 @@ import { Vehicle } from '../../features/vehicles/types/vehicles.types';
 interface AppState {
   // UI state
   sidebarOpen: boolean;
+  sidebarCollapsed: boolean;
   selectedVehicle: Vehicle | null;
 
   // Actions
   toggleSidebar: () => void;
   setSidebarOpen: (open: boolean) => void;
+  toggleSidebarCollapse: () => void;
   setSelectedVehicle: (vehicle: Vehicle | null) => void;
 }
 
+const savedCollapsed = localStorage.getItem('sidebarCollapsed') === 'true';
+
 export const useAppStore = create<AppState>((set) => ({
   // Initial state
   sidebarOpen: false,
+  sidebarCollapsed: savedCollapsed,
   selectedVehicle: null,
 
   // Actions
   toggleSidebar: () => set((state) => ({ sidebarOpen: !state.sidebarOpen })),
   setSidebarOpen: (open: boolean) => set({ sidebarOpen: open }),
+  toggleSidebarCollapse: () => set((state) => {
+    const next = !state.sidebarCollapsed;
+    localStorage.setItem('sidebarCollapsed', String(next));
+    return { sidebarCollapsed: next };
+  }),
   setSelectedVehicle: (vehicle: Vehicle | null) => set({ selectedVehicle: vehicle }),
 }));