Fix Traefik deployment: Replace SCRIPT_NAME with URL_PREFIX to avoid WSGI conflicts

[Copilot]

Problem

When deploying LocalCA behind Traefik with path prefix stripping (e.g., serving at /localca), users encounter this error:

Configuration problem: Request path '/' does not start with SCRIPT_NAME '/localca'

This prevents the application from working when deployed behind Traefik with the provided docker-compose-traefik.yml configuration.

Root Cause

The issue stems from a conflict between Django's URL generation and WSGI's request path validation:

1. The docker-compose-traefik.yml sets SCRIPT_NAME=/localca as an environment variable
2. Traefik strips the /localca prefix before forwarding requests to Django (as configured)
3. Django receives the request with path / (after stripping)
4. However, WSGI servers read SCRIPT_NAME from the environment and use it to validate incoming request paths
5. Django's CommonMiddleware checks if the request path starts with SCRIPT_NAME
6. The validation fails because '/' does not start with '/localca'

This is a fundamental incompatibility: you cannot use SCRIPT_NAME as an environment variable when the reverse proxy strips the prefix before forwarding requests.

Solution

This PR introduces a new environment variable URL_PREFIX to replace SCRIPT_NAME:

• URL_PREFIX is a custom variable that doesn't interfere with WSGI's path validation
• Django reads it only for the FORCE_SCRIPT_NAME setting, which controls URL generation
• Traefik can strip the prefix without causing validation errors
• Generated URLs still include the correct /localca prefix

Changes Made

1. settings.py: Changed from os.environ.get('SCRIPT_NAME') to os.environ.get('URL_PREFIX') with detailed comments explaining the change
2. docker-compose-traefik.yml: Updated environment variable from SCRIPT_NAME=/localca to URL_PREFIX=/localca
3. TRAEFIK_DEPLOYMENT.md: Updated all references and added a new section explaining the technical rationale
4. README.md: Updated reverse proxy deployment instructions

Migration Guide

Users deploying with Traefik should update their docker-compose-traefik.yml:

# Before (broken):
environment:
  - SCRIPT_NAME=/localca

# After (fixed):
environment:
  - URL_PREFIX=/localca

Then restart the container. No other changes are required.

Testing

• ✅ All 19 existing unit tests pass
• ✅ Integration testing confirms URL generation includes correct prefix
• ✅ Verified Django accepts requests without prefix (simulating Traefik stripping)
• ✅ Code passes pylint validation (10.00/10)
• ✅ docker-compose-traefik.yml syntax validated

Backward Compatibility

This change is fully backward compatible for:

• Deployments without a reverse proxy
• Deployments without path prefix requirements
• Any deployment not using docker-compose-traefik.yml

The only users affected are those already using docker-compose-traefik.yml with Traefik, who will need to update their configuration file as shown above.

Fixes #[issue_number]

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Docker compose and Traefik</issue_title>
<issue_description>If you use the docker compose configuration from the repository together with traefik, when you request the home page from the browser, the following error appears in the logs:
Configuration problem: Request path '/' does not start with SCRIPT_NAME '/localca'
The response to the browser is the same.

Traefik version 3.5.3</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #51

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