Add POI API routes and Celery task

FastAPI router with CRUD endpoints for POIs, distance calculation
trigger, and distance queries. Streaming GeoJSON endpoint now accepts
include_poi_distances=true to inject travel times into features.
Celery task wraps the distance calculator with progress reporting.

tasks/poi_tasks.py

@@ -0,0 +1,92 @@
+"""Celery tasks for POI distance calculation."""
+import asyncio
+import logging
+from typing import Any
+
+from celery import Task
+from celery_app import app
+from database import engine
+from models.listing import ListingType
+from repositories.listing_repository import ListingRepository
+from repositories.poi_repository import POIRepository
+from services.poi_distance_calculator import calculate_poi_distances
+
+logger = logging.getLogger("uvicorn.error")
+
+celery_logger = logging.getLogger("celery.task")
+if not celery_logger.handlers:
+    handler = logging.StreamHandler()
+    handler.setFormatter(logging.Formatter(
+        "%(asctime)s [%(levelname)s] %(name)s: %(message)s"
+    ))
+    celery_logger.addHandler(handler)
+    celery_logger.setLevel(logging.INFO)
+
+
+@app.task(bind=True)
+def calculate_poi_distances_task(
+    self: Task,
+    poi_id: int,
+    travel_modes: list[str],
+    listing_type: str,
+    listing_ids: list[int] | None = None,
+) -> dict[str, Any]:
+    """Background task to calculate distances from listings to a POI.
+
+    Args:
+        poi_id: ID of the PointOfInterest.
+        travel_modes: List of travel modes (WALK, BICYCLE, TRANSIT).
+        listing_type: "BUY" or "RENT".
+        listing_ids: Optional subset of listing IDs.
+    """
+    celery_logger.info(
+        f"Starting POI distance calculation: poi_id={poi_id}, "
+        f"modes={travel_modes}, type={listing_type}"
+    )
+
+    self.update_state(state="PROGRESS", meta={
+        "phase": "starting",
+        "progress": 0,
+        "message": "Starting distance calculation...",
+    })
+
+    listing_repo = ListingRepository(engine)
+    poi_repo = POIRepository(engine)
+
+    poi = poi_repo.get_poi_by_id(poi_id)
+    if poi is None:
+        celery_logger.error(f"POI {poi_id} not found")
+        return {"error": f"POI {poi_id} not found", "distances_computed": 0}
+
+    lt = ListingType(listing_type)
+
+    def on_progress(completed: int, total: int, message: str) -> None:
+        progress = round(completed / total, 2) if total > 0 else 0
+        self.update_state(state="PROGRESS", meta={
+            "phase": "computing",
+            "progress": progress,
+            "processed": completed,
+            "total": total,
+            "message": message,
+        })
+
+    total = asyncio.run(
+        calculate_poi_distances(
+            listing_repo=listing_repo,
+            poi_repo=poi_repo,
+            poi=poi,
+            travel_modes=travel_modes,
+            listing_type=lt,
+            listing_ids=listing_ids,
+            on_progress=on_progress,
+        )
+    )
+
+    celery_logger.info(f"POI distance calculation complete: {total} distances computed")
+
+    return {
+        "phase": "completed",
+        "progress": 1,
+        "distances_computed": total,
+        "message": f"Computed {total} distances for POI '{poi.name}'",
+    }