backend: Pydantic response_models für 5 GET-Endpoints hinzufügen

- health.py: HealthResponse
- eigenleben.py: EigenlebenOverviewResponse + SkillTextResponse
- chronik.py: ChronikResponse + ChronikItem
- wissen.py: WissenListResponse + WissenFileResponse
- reminders.py: ReminderListResponse + ReminderOut

py_compile bestanden, /docs zeigt neue Schemata.
Response-Payloads unverändert — nur Typisierung hinzugefügt.

backend/routers/health.py

@@ -1,5 +1,7 @@
 """Health-/Status-Endpoint — schlanker Lebenszeichen-Check für MC 2.0."""
 
+from pydantic import BaseModel
+
 from fastapi import APIRouter
 
 from config import VERSION
@@ -8,7 +10,15 @@ from services import gateway, llamaswap
 router = APIRouter(prefix="/api")
 
 
-@router.get("/health")
+class HealthResponse(BaseModel):
+    status: str
+    version: str
+    engine_reachable: bool
+    gateway_reachable: bool
+    brain: dict
+
+
+@router.get("/health", response_model=HealthResponse)
 def health() -> dict:
     return {
         "status": "ok",