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/models/place.py

@@ -0,0 +1,38 @@
+from datetime import datetime
+
+from geoalchemy2 import Geography
+from sqlalchemy import Boolean, DateTime, Enum, ForeignKey, String, Text, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.db.base import Base
+from app.models.enums import PlaceCategory
+
+
+class Place(Base):
+    __tablename__ = "places"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    city_id: Mapped[int] = mapped_column(ForeignKey("cities.id", ondelete="CASCADE"), nullable=False)
+    slug: Mapped[str] = mapped_column(String(128), unique=True, nullable=False)
+    category: Mapped[PlaceCategory] = mapped_column(
+        Enum(PlaceCategory, name="place_category", native_enum=True), nullable=False
+    )
+    location = mapped_column(
+        Geography(geometry_type="POINT", srid=4326, spatial_index=False), nullable=False
+    )
+    address: Mapped[str | None] = mapped_column(String(256))
+    district: Mapped[str | None] = mapped_column(String(128))
+    built_year: Mapped[str | None] = mapped_column(String(32))
+    architect_builder: Mapped[str | None] = mapped_column(String(256))
+    architectural_style: Mapped[str | None] = mapped_column(String(128))
+    notable_people: Mapped[str | None] = mapped_column(Text)
+    is_active: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now()
+    )
+
+    city: Mapped["City"] = relationship(back_populates="places")
+    contents: Mapped[list["PlaceContent"]] = relationship(
+        back_populates="place", cascade="all, delete-orphan"
+    )