chore: Replace Django 6.0a1 with 6.0 in test requirements

[vinitkumar]

Updates the test requirements to use Django 6.0 instead of 6.0a1

Summary by Sourcery

Update supported Python/Django matrix and tooling to target Python 3.10+ and Django up to 6.0, while modernizing CI, packaging metadata, and helper typings.

New Features:

• Add explicit support for Django 6.0 and new Python versions (3.13, 3.14) across tox and CI test matrices.

Enhancements:

• Raise the minimum supported Python version to 3.10 and refresh project classifiers and dependencies to match current support policy.
• Switch CI and lint workflows to use uv for dependency and tool installation, improving performance and consistency.
• Tighten type hints in helper utilities to use modern union syntax and more accurate parameter types.

Build:

• Adjust tox environments to drop legacy Django/Python combinations and add environments for Django 5.0–6.0 on Python 3.10–3.14.
• Add a new test requirements set for Django 6.0 with django CMS 5.0 and wire it into tox and GitHub Actions matrices.

CI:

• Expand GitHub Actions test matrices to cover newer Python versions and Django 6.0 combinations, removing unsupported combos.
• Update lint workflow to install and run ruff via uv instead of direct pip installs.
• Update the Django/CMS main-branch CI job to run against a Django 6.0-style requirements set on Python 3.13.

Documentation:

• Add AGENTS.md with guidance for AI assistants contributing to the project and document updated tooling and support ranges.

Tests:

• Align test requirements files and matrices with the new Django/Python support policy, including the new Django 6.0 requirements set.

Chores:

• Replace the django-fsm dependency with django-fsm-2 in project dependencies to reflect current usage.