feat: initial Skeen-CRM AI Agent architecture

- FastAPI + Python 3.12 backend
- Meta WhatsApp Business API client (official)
- OpenAI GPT-4o with function calling
- RAG vector store with pgvector
- ERPNext Frappe REST client
- Celery + Redis async task queue
- PostgreSQL with migrations (Alembic)
- Docker Compose full stack
- Enterprise logging, metrics, health checks

src/infrastructure/db.py

@@ -0,0 +1,62 @@
+"""Database configuration with async SQLAlchemy + pgvector."""
+
+from typing import AsyncGenerator
+
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+from sqlalchemy.orm import declarative_base
+from sqlalchemy.pool import NullPool
+
+from src.config import settings
+
+# Base class for SQLModel/SQLAlchemy models
+Base = declarative_base()
+
+# Engine configuration
+engine_kwargs = {
+    "pool_size": settings.DATABASE_POOL_SIZE,
+    "max_overflow": settings.DATABASE_MAX_OVERFLOW,
+    "pool_pre_ping": True,
+    "pool_recycle": 300,
+    "echo": settings.DEBUG,
+}
+
+if settings.APP_ENV == "testing":
+    engine_kwargs["poolclass"] = NullPool
+
+engine = create_async_engine(
+    settings.database_url_str,
+    **engine_kwargs,
+)
+
+# Session factory
+AsyncSessionLocal = async_sessionmaker(
+    engine,
+    class_=AsyncSession,
+    expire_on_commit=False,
+    autoflush=False,
+    autocommit=False,
+)
+
+
+async def get_db() -> AsyncGenerator[AsyncSession, None]:
+    """Yield an async database session for dependency injection."""
+    async with AsyncSessionLocal() as session:
+        try:
+            yield session
+            await session.commit()
+        except Exception:
+            await session.rollback()
+            raise
+        finally:
+            await session.close()
+
+
+async def init_db() -> None:
+    """Initialize database tables (for dev/testing only)."""
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+
+
+async def close_db() -> None:
+    """Dispose database engine."""
+    await engine.dispose()