Live AI provider/model switching without restart

Backend:
- RuntimeAIConfig singleton: mutable in-memory overrides for provider/model
- PATCH /admin/api/ai/config: change active provider/model on the fly
- GET /admin/api/ai/config: read current runtime state
- ai_vision.py: uses runtime_ai_config before falling back to settings
- health/status endpoints reflect runtime overrides

Frontend:
- 'Définir comme actif' button in AI config section
- Live feedback message on save

app/routers/admin_ai.py

@@ -17,6 +17,7 @@ from app.config import settings
 from app.database import get_db
 from app.dependencies.auth import require_scope
 from app.models.client import APIClient
+from app.services.runtime_config import runtime_ai_config
 
 logger = logging.getLogger(__name__)
 
@@ -114,13 +115,14 @@ def _build_providers() -> list[ProviderInfo]:
 @router.get("/status", response_model=AIStatusResponse)
 async def get_ai_status():
     """Retourne la configuration AI actuelle et les fournisseurs/modèles disponibles."""
-    active_model = (
-        settings.OPENROUTER_MODEL if settings.AI_PROVIDER == "openrouter"
+    active_provider = runtime_ai_config.provider or settings.AI_PROVIDER
+    active_model = runtime_ai_config.model or (
+        settings.OPENROUTER_MODEL if active_provider == "openrouter"
         else settings.GEMINI_MODEL
     )
     return AIStatusResponse(
         ai_enabled=settings.AI_ENABLED,
-        current_provider=settings.AI_PROVIDER,
+        current_provider=active_provider,
         current_model=active_model,
         providers=_build_providers(),
     )
@@ -252,3 +254,67 @@ async def _test_gemini(model: str, prompt: Optional[str], image_b64: Optional[st
         return {"success": True, "response": text[:500], "tokens": tokens}
     except Exception as e:
         return {"success": False, "error": str(e)[:500]}
+
+
+# ─────────────────────────────────────────────────────────────
+# GET /admin/api/ai/config  —  état actuel du runtime config
+# ─────────────────────────────────────────────────────────────
+
+@router.get("/config")
+async def get_runtime_config():
+    """Retourne la configuration AI runtime actuelle (provider + modèle)."""
+    return runtime_ai_config.to_dict()
+
+
+# ─────────────────────────────────────────────────────────────
+# PATCH /admin/api/ai/config  —  changer le provider/modèle live
+# ─────────────────────────────────────────────────────────────
+
+class UpdateAIConfigRequest(BaseModel):
+    provider: Optional[str] = Field(None, description="openrouter ou gemini")
+    model: Optional[str] = Field(None, description="Nom du modèle à activer")
+    reset: bool = Field(False, description="true = réinitialiser aux valeurs .env")
+
+class UpdateAIConfigResponse(BaseModel):
+    provider: str
+    model: str
+    is_overridden: bool
+    message: str
+
+
+@router.patch("/config", response_model=UpdateAIConfigResponse)
+async def update_runtime_config(
+    body: UpdateAIConfigRequest,
+    _=Depends(require_scope("admin")),
+):
+    """Change le fournisseur et/ou le modèle AI actif sans redémarrer."""
+    if body.reset:
+        runtime_ai_config.clear()
+        state = runtime_ai_config.to_dict()
+        return UpdateAIConfigResponse(
+            provider=state["provider"],
+            model=state["model"],
+            is_overridden=False,
+            message="Configuration AI réinitialisée aux valeurs .env",
+        )
+
+    if not body.provider and not body.model:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="Spécifiez provider et/ou model, ou reset=true",
+        )
+
+    runtime_ai_config.set(provider=body.provider, model=body.model)
+    state = runtime_ai_config.to_dict()
+
+    logger.info("ai.runtime_config.updated", extra={
+        "provider": state["provider"],
+        "model": state["model"],
+    })
+
+    return UpdateAIConfigResponse(
+        provider=state["provider"],
+        model=state["model"],
+        is_overridden=True,
+        message=f"Fournisseur changé à {state['provider']}, modèle {state['model']}",
+    )