feat: database models and Alembic migrations — User, Recording, Transcription, Protocol, PromptTemplate, ExportFile

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/database.py

@@ -0,0 +1,11 @@
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+
+from app.config import settings
+
+engine = create_async_engine(settings.database_url, echo=False)
+async_session = async_sessionmaker(engine, expire_on_commit=False)
+
+
+async def get_db():
+    async with async_session() as session:
+        yield session