feat(M6): Weitere Hosts — MiniApps in Fenstern + AI-Agenten-Ausgabe-Bloecke (#364)

- Windows-Host: openMiniAppWindow-Helper + MiniAppWindowContent (windowStore);
  Oeffnen-Buttons im Chat-Block (MiniAppBlock) und Dashboard-Widget
- AI-Agenten-Host: Core-Tool send_miniapp (app/ai/miniapp_tools.py) —
  miniapp-Block in Agent-Chat (approval_request-Praezedenz), Permission
  fail-closed gegen aufrufenden User pro App; Registrierung im lifespan
- agent_loop: tool_context + agent_name (Raum-Aufloesung)
- Fix: MiniAppBlock nutzt useMiniapps (component-Feld) statt Legacy /comm/miniapps
- Tests: M6 7/7 (TDD rot->gruen), Backend-Regression 57/57, Vitest 26/26
  (4 neue Window-Tests), tsc clean, build OK

app/main.py

@@ -223,6 +223,11 @@ async def lifespan(app: FastAPI):
 
     register_system_miniapps()
 
+    # Core AI agent tools for MiniApp output (Phase M6)
+    from app.ai.miniapp_tools import register_miniapp_tools
+
+    register_miniapp_tools()
+
     # Install discovered builtin plugins and activate only those marked active in DB
     from sqlalchemy import select as sa_select
     from sqlalchemy.ext.asyncio import async_sessionmaker