fix: Add setuptools constraint to requirements.txt for gunicorn compatibility

API server was crashing with 'ModuleNotFoundError: No module named pkg_resources'
because gunicorn requires pkg_resources from setuptools, but setuptools 73+
removed this module.

The constraint was already in requirements-webapp.txt for the client, but
requirements.txt (used by API/worker containers) was missing it, causing
the API container to fail on startup.

Root cause: docker/app/Dockerfile installs both requirements-webapp.txt AND
requirements.txt, but the latter lacked the setuptools constraint, allowing
pip to install setuptools 73+ which doesn't provide pkg_resources.

Fix: Add setuptools>=65.5.0,<73.0.0 to requirements.txt to ensure pkg_resources
is available for gunicorn in Python 3.9 API/worker containers.

Fixes: Integration test failures where API container exits with code 1

Author: dahagag

requirements.txt

@@ -1,6 +1,7 @@
 Flask==2.2.1
 Flask-Cors==3.0.10
 Pillow==10.4.0  # 10.1.0+ required for Python 3.13 support
+setuptools>=65.5.0,<73.0.0  # Required for pkg_resources (gunicorn dependency). setuptools 73+ removed pkg_resources
 apache-libcloud==3.6.0
 applicationinsights==0.11.10
 beautifulsoup4==4.11.1