Add structured logging throughout the backend

Request-level logging middleware (method/path/status/duration),
per-module loggers in routes/services (nearby search radius
expansion, 404s, name search), LOG_LEVEL setting wired through
docker-compose, and seed_loader converted from print() to logging.

Verified: pytest passes, and manually confirmed log lines appear for
both successful and 404 requests via `docker compose logs api`.

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

docker-compose.yml

@@ -19,6 +19,7 @@ services:
     build: ./backend
     environment:
       DATABASE_URL: postgresql+psycopg://${POSTGRES_USER}:${POSTGRES_PASSWORD}@db:5432/${POSTGRES_DB}
+      LOG_LEVEL: ${LOG_LEVEL:-INFO}
     ports:
       - "8000:8000"
     depends_on: