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/__init__.py

@@ -0,0 +1,5 @@
+from app.models.city import City
+from app.models.place import Place
+from app.models.place_content import PlaceContent
+
+__all__ = ["City", "Place", "PlaceContent"]

backend/app/models/city.py

@@ -0,0 +1,23 @@
+from datetime import datetime
+
+from geoalchemy2 import Geography
+from sqlalchemy import DateTime, String, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.db.base import Base
+
+
+class City(Base):
+    __tablename__ = "cities"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    slug: Mapped[str] = mapped_column(String(64), unique=True, nullable=False)
+    name_ru: Mapped[str] = mapped_column(String(128), nullable=False)
+    name_en: Mapped[str] = mapped_column(String(128), nullable=False)
+    country_code: Mapped[str] = mapped_column(String(2), nullable=False, default="RU")
+    center_point = mapped_column(
+        Geography(geometry_type="POINT", srid=4326, spatial_index=False), nullable=True
+    )
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+
+    places: Mapped[list["Place"]] = relationship(back_populates="city", cascade="all, delete-orphan")

backend/app/models/enums.py

@@ -0,0 +1,25 @@
+import enum
+
+
+class PlaceCategory(str, enum.Enum):
+    building = "building"
+    bridge = "bridge"
+    monument = "monument"
+    park = "park"
+    district = "district"
+    skyscraper = "skyscraper"
+    cathedral = "cathedral"
+    museum = "museum"
+    gate = "gate"
+    square = "square"
+
+
+class ContentLanguage(str, enum.Enum):
+    ru = "ru"
+    en = "en"
+
+
+class ContentLength(str, enum.Enum):
+    short = "short"
+    medium = "medium"
+    long = "long"

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"
+    )

backend/app/models/place_content.py

@@ -0,0 +1,23 @@
+from sqlalchemy import Enum, ForeignKey, String, Text, UniqueConstraint
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.db.base import Base
+from app.models.enums import ContentLanguage, ContentLength
+
+
+class PlaceContent(Base):
+    __tablename__ = "place_content"
+    __table_args__ = (UniqueConstraint("place_id", "language", "length", name="uq_place_content_variant"),)
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    place_id: Mapped[int] = mapped_column(ForeignKey("places.id", ondelete="CASCADE"), nullable=False)
+    language: Mapped[ContentLanguage] = mapped_column(
+        Enum(ContentLanguage, name="content_language", native_enum=True), nullable=False
+    )
+    length: Mapped[ContentLength] = mapped_column(
+        Enum(ContentLength, name="content_length", native_enum=True), nullable=False
+    )
+    title: Mapped[str] = mapped_column(String(256), nullable=False)
+    body: Mapped[str] = mapped_column(Text, nullable=False)
+
+    place: Mapped["Place"] = relationship(back_populates="contents")