feat(M4): System-Rueckbau — Dashboard-Inhalte als MiniApps, Core = reiner Host (#362)

- system_miniapps.py: audit_activity (audit:read, settings max_items) + system_metrics (settings:read) als Core-Apps in Registry
- base.py-Fix: native Manifest-MiniApps reichen component durch (M1-Luecke)
- contacts-Manifest: contacts_stats (ContactsStatsWidget, contacts:read, show_companies/show_persons)
- Seed-Fix: nur renderbare Apps (component) landen im Dashboard-Layout
- Frontend: ContactsStatsWidget, AuditActivityWidget, SystemMetricsWidget; MiniAppHost-Registry +3
- Dashboard.tsx = reiner Host (26 Z.); Page-Tests auf Pure-Host umgeschrieben
- Tests: M4 7/7 (TDD rot->gruen), Backend-Regression 46/46, Vitest 22/22, tsc clean, build OK

app/routes/dashboards.py

@@ -110,7 +110,9 @@ async def _seed_default_dashboard(
     apps = [
         a
         for a in registry.list_apps(host="dashboard")
-        if user_permits(current_user, a) and "dashboard" in (a.get("hosts") or [])
+        if user_permits(current_user, a)
+        and "dashboard" in (a.get("hosts") or [])
+        and a.get("component")  # renderable only (M4: chat apps stay off layouts)
     ]
     apps.sort(key=lambda a: a.get("order", 100))