Add FastAPI backend with PostGIS-backed nearby search

FastAPI service backed by PostgreSQL+PostGIS: cities/places/place_content
schema (normalized per-language, per-length content for easy future
re-ingestion), Alembic migration, an iterative-radius-expansion nearby
search endpoint, a name-search fallback for denied-location flows, and
a YAML seed loader CLI. Verified end-to-end against a live Docker
Postgres+PostGIS instance (migration, city seed, place/content CRUD,
and nearby radius expansion all confirmed working via curl).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/app/core/logging.py

@@ -0,0 +1,8 @@
+import logging
+
+
+def configure_logging(level: int = logging.INFO) -> None:
+    logging.basicConfig(
+        level=level,
+        format="%(asctime)s %(levelname)s %(name)s %(message)s",
+    )