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

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

backend/app/models/base.py

@@ -0,0 +1,21 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import DateTime, func
+from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+class TimestampMixin:
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now()
+    )
+
+
+class UUIDMixin:
+    id: Mapped[uuid.UUID] = mapped_column(
+        primary_key=True, default=uuid.uuid4
+    )