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.

app/plugins/builtins/marketplace/plugin.py

@@ -5,7 +5,7 @@ from __future__ import annotations
 import logging
 
 from app.plugins.base import BasePlugin
-from app.plugins.manifest import PluginManifest, PluginRouteDef
+from app.plugins.manifest import FrontendMenuItem, FrontendPageRoute, PluginManifest, PluginRouteDef
 
 logger = logging.getLogger(__name__)
 
@@ -29,8 +29,26 @@ class MarketplacePlugin(BasePlugin):
         events=[],
         migrations=["0001_initial.sql"],
         permissions=["marketplace:read", "marketplace:admin"],
-        menu_items=[],
-        page_routes=[],
+        # UI-Backlog Modul 5 (2026-09-13): marketplace browse/install page,
+        # registered via the manifest (Phase Q pattern).
+        menu_items=[
+            FrontendMenuItem(
+                label_key="nav.marketplace",
+                label="Marketplace",
+                path="/marketplace",
+                icon="Store",
+                order=85,
+                permission="marketplace:read",
+            ),
+        ],
+        page_routes=[
+            FrontendPageRoute(
+                path="/marketplace",
+                component="@/pages/Marketplace",
+                protected=True,
+                permission="marketplace:read",
+            ),
+        ],
         settings_pages=[],
         detail_tabs=[],
         author="LeoCRM",