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/alembic/versions/0001_init_schema.py

@@ -0,0 +1,115 @@
+"""init schema
+
+Revision ID: 0001
+Revises:
+Create Date: 2026-07-09
+
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+from geoalchemy2 import Geography
+from sqlalchemy.dialects import postgresql
+
+revision: str = "0001"
+down_revision: Union[str, None] = None
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.execute("CREATE EXTENSION IF NOT EXISTS postgis")
+
+    bind = op.get_bind()
+
+    place_category = postgresql.ENUM(
+        "building",
+        "bridge",
+        "monument",
+        "park",
+        "district",
+        "skyscraper",
+        "cathedral",
+        "museum",
+        "gate",
+        "square",
+        name="place_category",
+        create_type=False,
+    )
+    content_language = postgresql.ENUM("ru", "en", name="content_language", create_type=False)
+    content_length = postgresql.ENUM("short", "medium", "long", name="content_length", create_type=False)
+
+    place_category.create(bind, checkfirst=True)
+    content_language.create(bind, checkfirst=True)
+    content_length.create(bind, checkfirst=True)
+
+    op.create_table(
+        "cities",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column("slug", sa.String(64), nullable=False, unique=True),
+        sa.Column("name_ru", sa.String(128), nullable=False),
+        sa.Column("name_en", sa.String(128), nullable=False),
+        sa.Column("country_code", sa.String(2), nullable=False, server_default="RU"),
+        sa.Column(
+            "center_point",
+            Geography(geometry_type="POINT", srid=4326, spatial_index=False),
+            nullable=True,
+        ),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+    )
+
+    op.create_table(
+        "places",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column("city_id", sa.Integer(), sa.ForeignKey("cities.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("slug", sa.String(128), nullable=False, unique=True),
+        sa.Column("category", place_category, nullable=False),
+        sa.Column(
+            "location",
+            Geography(geometry_type="POINT", srid=4326, spatial_index=False),
+            nullable=False,
+        ),
+        sa.Column("address", sa.String(256), nullable=True),
+        sa.Column("district", sa.String(128), nullable=True),
+        sa.Column("built_year", sa.String(32), nullable=True),
+        sa.Column("architect_builder", sa.String(256), nullable=True),
+        sa.Column("architectural_style", sa.String(128), nullable=True),
+        sa.Column("notable_people", sa.Text(), nullable=True),
+        sa.Column("is_active", sa.Boolean(), nullable=False, server_default=sa.true()),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+    )
+    op.create_index("idx_places_location_gist", "places", ["location"], postgresql_using="gist")
+    op.create_index("idx_places_city_id", "places", ["city_id"])
+
+    op.create_table(
+        "place_content",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column("place_id", sa.Integer(), sa.ForeignKey("places.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("language", content_language, nullable=False),
+        sa.Column("length", content_length, nullable=False),
+        sa.Column("title", sa.String(256), nullable=False),
+        sa.Column("body", sa.Text(), nullable=False),
+        sa.UniqueConstraint("place_id", "language", "length", name="uq_place_content_variant"),
+    )
+    op.create_index("idx_place_content_lookup", "place_content", ["place_id", "language", "length"])
+
+
+def downgrade() -> None:
+    op.drop_index("idx_place_content_lookup", table_name="place_content")
+    op.drop_table("place_content")
+    op.drop_index("idx_places_city_id", table_name="places")
+    op.drop_index("idx_places_location_gist", table_name="places")
+    op.drop_table("places")
+    op.drop_table("cities")
+
+    bind = op.get_bind()
+    postgresql.ENUM(name="content_length").drop(bind, checkfirst=True)
+    postgresql.ENUM(name="content_language").drop(bind, checkfirst=True)
+    postgresql.ENUM(name="place_category").drop(bind, checkfirst=True)
+
+    # Deliberately not dropping the postgis extension: the postgis/postgis base
+    # image pre-installs postgis_topology/postgis_tiger_geocoder which depend on
+    # it, and dropping a shared extension here is out of this migration's scope.