Replace uv package manager with standard pip for dependency management.
Switch base image from debian:bookworm-slim to python:3.12-slim to include
Python runtime by default.
Key changes:
- Remove uv installation and configuration
- Use requirements.txt instead of pyproject.toml/uv.lock
- Install dependencies with pip instead of uv sync
- Move collectstatic and migrate from build-time to runtime in CMD
- Simplify gunicorn command invocation
This simplifies the build process and makes the image more portable by
using standard Python tooling. Running migrations and collectstatic at
container startup ensures they execute against the correct database and
storage backend.
