prod(docker): support BASE_IMAGE override for both stages; enable BuildKit pip cache; compose uses Dockerfile.production

Dockerfile.production

@@ -1,5 +1,7 @@
+# syntax=docker/dockerfile:1.5
 # Production Dockerfile for Delphi Consulting Group Database System
-FROM python:3.12-slim as builder
+ARG BASE_IMAGE=python:3.12-slim
+FROM ${BASE_IMAGE} as builder
 
 # Set build arguments
 ARG BUILD_DATE
@@ -19,10 +21,12 @@ WORKDIR /app
 
 # Copy requirements and install dependencies
 COPY requirements.txt .
-RUN pip install --no-cache-dir --user -r requirements.txt
+RUN --mount=type=cache,target=/root/.cache/pip \
+    pip install --user -r requirements.txt
 
 # Production stage
-FROM python:3.12-slim
+ARG BASE_IMAGE=python:3.12-slim
+FROM ${BASE_IMAGE}
 
 # Set labels
 LABEL maintainer="Delphi Consulting Group Inc." \