Refactor Dockerfile to use setuptools build

The Docker build was failing in the CI/CD pipeline because it was attempting to use Poetry to export dependencies, but the project is configured to use setuptools.

This commit refactors the Dockerfile to use a standard, multi-stage build process with setuptools. The builder stage now creates a Python wheel, which is then installed in the runtime stage. This resolves the build error and correctly installs the application and its dependencies.

Additionally, the `build` package version has been pinned to `1.3.0` to satisfy the `hadolint` pre-commit hook.

Author: google-labs-jules[bot]

Dockerfile

@@ -2,7 +2,7 @@
 FROM python:3.12-slim AS builder
 
 # Install build dependencies
-RUN pip install --no-cache-dir build
+RUN pip install --no-cache-dir build==1.3.0
 
 # Set the working directory
 WORKDIR /app