feat(04-01): implement marketplace page and marketplace-store

Create marketplace-store (Zustand) with sidebarRefreshKey signal and
tenant context. Build /marketplace page with parallel fetch, activation
Map, role gate, empty state, and responsive card grid. All 9 tests pass.

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

apps/web/src/lib/stores/marketplace-store.ts

@@ -0,0 +1,15 @@
+import { create } from 'zustand';
+
+interface MarketplaceState {
+  sidebarRefreshKey: number;
+  bumpSidebarRefresh: () => void;
+  selectedTenantId: string | null;
+  setSelectedTenantId: (id: string | null) => void;
+}
+
+export const useMarketplaceStore = create<MarketplaceState>()((set) => ({
+  sidebarRefreshKey: 0,
+  bumpSidebarRefresh: () => set((state) => ({ sidebarRefreshKey: state.sidebarRefreshKey + 1 })),
+  selectedTenantId: null,
+  setSelectedTenantId: (id) => set({ selectedTenantId: id }),
+}));