fix(FN-002): address Dockerfile build order, base images, .dockerignore, docs

apps/api/.dockerignore

@@ -0,0 +1,15 @@
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+.venv/
+venv/
+ENV/
+env/
+*.egg-info/
+dist/
+build/
+.git/
+.env
+.env.local
+*.log

apps/api/Dockerfile

@@ -1,15 +1,14 @@
-FROM python:3.14-slim
+FROM python:3.12-slim
 
 WORKDIR /app
 
 ENV PYTHONDONTWRITEBYTECODE=1
 ENV PYTHONUNBUFFERED=1
 
+COPY app/ ./app/
 COPY pyproject.toml ./
 RUN pip install --no-cache-dir -e ".[dev]"
 
-COPY app/ ./app/
-
 EXPOSE 8000
 
 CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]