fix: add PYTHONPATH and __init__.py for alembic to find app module

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: baijum

app/Dockerfile

@@ -9,6 +9,8 @@ RUN pip install --no-cache-dir -r requirements.txt
 
 COPY app/ ./app/
 
+ENV PYTHONPATH=/app
+
 EXPOSE 8000
 
 CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]