feat(marketplace): UI fuer Plugin-Marketplace — Modul 5/16 des UI-Backlogs

ERSTES Modul ueber die Phase-Q-Plugin-Architektur: Registrierung komplett
ueber das Plugin-Manifest (page_routes + menu_items) — routes/index.tsx und
Sidebar.tsx wurden NICHT angefasst. Der Komponenten-Map-Generator wired den
lazy import automatisch (38 Komponenten).

Backend existierte vollstaendig (listings mit search/tags/pagination,
listing-detail, install mit Ed25519-Signatur-Verify, verify, categories;
marketplace:read/admin + require_admin fuer Install), Frontend hatte 0%
Abdeckung.

- api/marketplace.ts: TanStack-Hooks (useMarketplaceListings mit
  search/tags/pagination, useMarketplaceListing, useMarketplaceCategories,
  useInstallFromMarketplace, useVerifyMarketplacePlugin)
- pages/Marketplace.tsx: Suche, Tag-Filter-Chips, Listing-Karten (Name,
  Version, Author, Beschreibung, Tags, Download-Counter, Verified-Badge,
  Preis/Kostenlos), Install mit Confirm (Admin-only via is_system_admin),
  Signatur-Verify, Ergebnis-Banner, Pagination — No-Access-Card ohne
  marketplace:read
- Manifest: page_route /marketplace + menu_item (Store-Icon, order 85,
  permission marketplace:read)
- i18n marketplace.* + nav.marketplace de/en

Verifikation: Vitest 10/10 (Rendering, No-Access, Empty/Error, Karten,
  Search+Tags, Admin-Gating, Install-Flow mit+ohne Confirm, Verify-Flow) ·
  tsc exit 0 · production build exit 0 · Backend-Regressionen
  (route-order, m5-miniapps) 10/10 · compileall sauber · Manifest-Check:
  page_route + menu_item korrekt.

frontend/src/api/marketplace.ts

@@ -0,0 +1,136 @@
+/**
+ * Marketplace API client — browse, search, verify and install plugins.
+ *
+ * Backend: /api/v1/marketplace (listings, listing detail, install, verify,
+ * categories). Permissions: marketplace:read (browse/verify), admin
+ * (install).
+ */
+
+import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
+import { apiGet, apiPost } from '@/api/client';
+
+export interface MarketplaceListing {
+  id: string;
+  name: string;
+  display_name: string;
+  description: string;
+  version: string;
+  author: string;
+  homepage: string;
+  download_url: string;
+  icon: string;
+  screenshots: string[];
+  tags: string[];
+  price: number;
+  is_verified: boolean;
+  download_count: number;
+  min_app_version: string;
+  license: string;
+  created_at: string | null;
+  updated_at: string | null;
+}
+
+export interface MarketplaceListResponse {
+  listings: MarketplaceListing[];
+  total: number;
+  page: number;
+  page_size: number;
+}
+
+export interface MarketplaceCategoriesResponse {
+  categories: string[];
+  total: number;
+}
+
+export interface MarketplaceInstallResponse {
+  success: boolean;
+  name: string;
+  display_name: string;
+  version: string;
+  installed: boolean;
+  activated: boolean;
+  message: string;
+  error: string | null;
+}
+
+export interface MarketplaceVerifyResponse {
+  name: string;
+  version: string;
+  signature_valid: boolean;
+  message: string;
+}
+
+export interface MarketplaceListParams {
+  search?: string;
+  tags?: string[];
+  page?: number;
+  pageSize?: number;
+}
+
+// ─── Query hooks ─────────────────────────────────────────────
+
+export function useMarketplaceListings(params: MarketplaceListParams = {}) {
+  const searchParams = new URLSearchParams();
+  if (params.search) searchParams.set('search', params.search);
+  if (params.tags && params.tags.length > 0) searchParams.set('tags', params.tags.join(','));
+  if (params.page) searchParams.set('page', String(params.page));
+  if (params.pageSize) searchParams.set('page_size', String(params.pageSize));
+  const qs = searchParams.toString();
+
+  return useQuery<MarketplaceListResponse>({
+    queryKey: ['marketplace-listings', params.search, params.tags, params.page, params.pageSize],
+    queryFn: () => apiGet<MarketplaceListResponse>(`/marketplace/listings${qs ? `?${qs}` : ''}`),
+  });
+}
+
+export function useMarketplaceListing(name: string | null) {
+  return useQuery<MarketplaceListing>({
+    queryKey: ['marketplace-listings', name],
+    queryFn: () => apiGet<MarketplaceListing>(`/marketplace/listings/${name}`),
+    enabled: !!name,
+  });
+}
+
+export function useMarketplaceCategories() {
+  return useQuery<MarketplaceCategoriesResponse>({
+    queryKey: ['marketplace-categories'],
+    queryFn: () => apiGet<MarketplaceCategoriesResponse>('/marketplace/categories'),
+  });
+}
+
+// ─── Mutation hooks ──────────────────────────────────────────
+
+export function useInstallFromMarketplace() {
+  const qc = useQueryClient();
+  return useMutation<
+    MarketplaceInstallResponse,
+    Error,
+    { name: string; signature?: string; publicKey?: string; activate?: boolean }
+  >({
+    mutationFn: ({ name, signature, publicKey, activate }) =>
+      apiPost<MarketplaceInstallResponse>(`/marketplace/install/${name}`, {
+        name,
+        signature: signature ?? null,
+        public_key: publicKey ?? null,
+        activate: activate ?? false,
+      }),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ['marketplace-listings'] });
+    },
+  });
+}
+
+export function useVerifyMarketplacePlugin() {
+  return useMutation<
+    MarketplaceVerifyResponse,
+    Error,
+    { name: string; signature?: string; publicKey?: string }
+  >({
+    mutationFn: ({ name, signature, publicKey }) =>
+      apiPost<MarketplaceVerifyResponse>(`/marketplace/verify/${name}`, {
+        name,
+        signature: signature ?? null,
+        public_key: publicKey ?? null,
+      }),
+  });
+}