feat: add combined environment endpoint for concurrent weather + air quality fetch

- POST /volatile/fetch/environment/{city} fetches both in parallel
- Single geocode lookup shared between API calls
- Uses asyncio.gather() for concurrent external requests
- Fix scheduler executor name (rest_api → rest_api_executor)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/routers/volatile.py

@@ -545,6 +545,64 @@ async def fetch_air_quality(
     }
 
 
+@router.post("/fetch/environment/{city}")
+async def fetch_environment(
+    city: str,
+    user: str = Query(default=DEFAULT_USER, description="User identifier"),
+    weather_ttl: int = Query(default=3600, ge=60, le=86400, description="Weather TTL in seconds"),
+    air_quality_ttl: int = Query(default=3600, ge=60, le=86400, description="Air quality TTL in seconds"),
+    qdrant: QdrantDep = None,
+    ollama: OllamaDep = None,
+    api_key: str = Depends(verify_api_key)
+):
+    """
+    Fetch weather and air quality concurrently for a city.
+
+    Performs a single geocode lookup and fetches both weather and air quality
+    data in parallel, storing both in volatile cache. More efficient than
+    calling /fetch/weather and /fetch/air_quality separately.
+
+    **Example:**
+    ```
+    POST /volatile/fetch/environment/rotterdam?user=jpmschweitzer
+    ```
+
+    **Response includes:**
+    - weather: Current conditions (temperature, humidity, wind, UV)
+    - air_quality: AQI indices, pollutants, pollen data
+    """
+    volatile_service = get_volatile_service(qdrant, ollama)
+    weather_provider = get_weather_provider()
+
+    fetch_service = VolatileFetchService(
+        volatile_service=volatile_service,
+        weather_provider=weather_provider,
+    )
+
+    result = await fetch_service.fetch_environment(
+        user, city, weather_ttl=weather_ttl, air_quality_ttl=air_quality_ttl
+    )
+
+    if not result.success:
+        raise HTTPException(status_code=500, detail="; ".join(result.errors))
+
+    return {
+        "success": True,
+        "key": result.key,
+        "weather": {
+            "success": result.weather.success if result.weather else False,
+            "record": result.weather.record if result.weather else None,
+            "error": result.weather.error if result.weather else None,
+        },
+        "air_quality": {
+            "success": result.air_quality.success if result.air_quality else False,
+            "record": result.air_quality.record if result.air_quality else None,
+            "error": result.air_quality.error if result.air_quality else None,
+        },
+        "errors": result.errors,
+    }
+
+
 @router.get("/{namespace}/{key}", response_model=VolatileRecordResponse)
 async def get_record(
     namespace: str,