Initial Aurora Core 0.1 implementation

Production-grade media metadata backend per docs/aurora-core-spec.md:
Aurora-owned UUIDv7 identity system, normalized movie/TV/people/credits
schema, provider abstraction with a TMDb adapter, an idempotent async
ingestion pipeline (normalize -> match -> upsert -> provenance), a
Postgres FTS/trigram search layer, a stateless FastAPI v1 API with
Redis caching/rate-limiting, arq workers, dev/prod Docker Compose
topologies, unit + integration + load tests, CI, and architecture/
database/API/ERD documentation.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

app/core/database.py

@@ -0,0 +1,88 @@
+"""Async SQLAlchemy engine/session management.
+
+The API is stateless: every request gets its own AsyncSession from a shared
+connection pool, and nothing is held across requests. This module never
+creates tables — schema changes always go through Alembic (see
+`migrations/`).
+"""
+
+from __future__ import annotations
+
+from collections.abc import AsyncGenerator
+from contextlib import asynccontextmanager
+
+from sqlalchemy.ext.asyncio import (
+    AsyncEngine,
+    AsyncSession,
+    async_sessionmaker,
+    create_async_engine,
+)
+
+from app.core.config import get_settings
+
+settings = get_settings()
+
+_connect_args: dict = {}
+if settings.DATABASE_BEHIND_TRANSACTION_POOLER:
+    _connect_args["statement_cache_size"] = 0
+
+_engine: AsyncEngine = create_async_engine(
+    settings.DATABASE_URL,
+    pool_size=settings.DATABASE_POOL_SIZE,
+    max_overflow=settings.DATABASE_MAX_OVERFLOW,
+    pool_pre_ping=True,
+    pool_recycle=1800,
+    connect_args=_connect_args,
+    echo=False,
+)
+
+async_session_factory = async_sessionmaker(
+    bind=_engine,
+    class_=AsyncSession,
+    expire_on_commit=False,
+    autoflush=False,
+)
+
+
+def get_engine() -> AsyncEngine:
+    return _engine
+
+
+async def get_db() -> AsyncGenerator[AsyncSession, None]:
+    """FastAPI dependency yielding a request-scoped session."""
+
+    async with async_session_factory() as session:
+        yield session
+
+
+@asynccontextmanager
+async def session_scope() -> AsyncGenerator[AsyncSession, None]:
+    """Context manager for use outside request handlers (workers, scripts).
+
+    Commits on success, rolls back on exception.
+    """
+
+    async with async_session_factory() as session:
+        try:
+            yield session
+            await session.commit()
+        except Exception:
+            await session.rollback()
+            raise
+
+
+async def database_is_ready() -> bool:
+    """Cheap connectivity check used by the /ready endpoint."""
+
+    from sqlalchemy import text
+
+    try:
+        async with _engine.connect() as conn:
+            await conn.execute(text("SELECT 1"))
+        return True
+    except Exception:
+        return False
+
+
+async def dispose_engine() -> None:
+    await _engine.dispose()