feat(database): add simplified database session module

Lightweight database session implementation:
- Basic connection management
- Simplified query execution
- Development and testing support
- Alternative to full ORM overhead

src/db/simple_session.py

@@ -0,0 +1,50 @@
+"""
+Simple database session management for SQLite.
+"""
+
+import os
+from contextlib import asynccontextmanager
+from typing import AsyncGenerator
+
+from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine, async_sessionmaker
+from dotenv import load_dotenv
+
+load_dotenv()
+
+# Get DATABASE_URL from environment
+DATABASE_URL = os.getenv("DATABASE_URL", "sqlite+aiosqlite:///./cidadao_ai.db")
+
+# Create async engine
+engine = create_async_engine(
+    DATABASE_URL,
+    echo=False,
+    pool_pre_ping=True,
+)
+
+# Create session factory
+AsyncSessionLocal = async_sessionmaker(
+    engine,
+    class_=AsyncSession,
+    expire_on_commit=False,
+)
+
+
+@asynccontextmanager
+async def get_db_session() -> AsyncGenerator[AsyncSession, None]:
+    """Get database session context manager."""
+    async with AsyncSessionLocal() as session:
+        try:
+            yield session
+            await session.commit()
+        except Exception:
+            await session.rollback()
+            raise
+        finally:
+            await session.close()
+
+
+# Alias for FastAPI dependency
+async def get_db() -> AsyncGenerator[AsyncSession, None]:
+    """FastAPI dependency for database session."""
+    async with get_db_session() as session:
+        yield session