Update .dockerignore, alembic revision, and entrypoint script for consistency and reliability

- Expanded `.dockerignore` to exclude Python and packaging-related artifacts for cleaner Docker builds.
- Updated Alembic `down_revision` in migration script to reflect correct dependency chain.
- Modified entrypoint script to use `uv` with `--no-project` flag, preventing permission issues in bind-mounted volumes.

backend/.dockerignore

@@ -1,2 +1,17 @@
 .venv
-*.iml
+*.iml
+
+# Python build and cache artifacts
+__pycache__/
+.pytest_cache/
+.mypy_cache/
+.ruff_cache/
+*.pyc
+*.pyo
+
+# Packaging artifacts
+*.egg-info/
+build/
+dist/
+htmlcov/
+.uv_cache/