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/i18n/locales/de.json

@@ -23,7 +23,8 @@
     "wiki": "Wiki",
     "systemDashboard": "System Dashboard",
     "approvals": "Freigaben",
-    "delegations": "Delegationen"
+    "delegations": "Delegationen",
+    "marketplace": "Marketplace"
   },
   "auth": {
     "login": "Anmelden",
@@ -1705,5 +1706,22 @@
     "defaultBadge": "Standard",
     "empty": "Keine Mandanten vorhanden.",
     "loadError": "Mandanten konnten nicht geladen werden."
+  },
+  "marketplace": {
+    "title": "Marketplace",
+    "searchPlaceholder": "Plugins durchsuchen...",
+    "categories": "Kategorien",
+    "allTags": "Alle",
+    "free": "Kostenlos",
+    "verified": "Verifiziert",
+    "install": "Installieren",
+    "installConfirm": "Plugin '{{name}}' wirklich installieren und aktivieren?",
+    "installSuccess": "Plugin '{{name}}' erfolgreich installiert.",
+    "installFailed": "Installation fehlgeschlagen",
+    "verify": "Signatur pruefen",
+    "verifyFailed": "Signaturpruefung fehlgeschlagen",
+    "empty": "Keine Plugins gefunden.",
+    "loadError": "Marketplace konnte nicht geladen werden.",
+    "noAccess": "Kein Zugriff auf den Marketplace (marketplace:read noetig)."
   }
 }

frontend/src/i18n/locales/en.json

@@ -23,7 +23,8 @@
     "wiki": "Wiki",
     "systemDashboard": "System Dashboard",
     "approvals": "Approvals",
-    "delegations": "Delegations"
+    "delegations": "Delegations",
+    "marketplace": "Marketplace"
   },
   "auth": {
     "login": "Sign In",
@@ -1705,5 +1706,22 @@
     "defaultBadge": "Default",
     "empty": "No tenants yet.",
     "loadError": "Failed to load tenants."
+  },
+  "marketplace": {
+    "title": "Marketplace",
+    "searchPlaceholder": "Search plugins...",
+    "categories": "Categories",
+    "allTags": "All",
+    "free": "Free",
+    "verified": "Verified",
+    "install": "Install",
+    "installConfirm": "Really install and activate plugin '{{name}}'?",
+    "installSuccess": "Plugin '{{name}}' installed successfully.",
+    "installFailed": "Installation failed",
+    "verify": "Verify signature",
+    "verifyFailed": "Signature verification failed",
+    "empty": "No plugins found.",
+    "loadError": "Failed to load the marketplace.",
+    "noAccess": "No marketplace access (marketplace:read required)."
   }
 }