[AdrianDAlessandro]

Description

This PR adds Django Guardian as a requirement, along with some signals and custom permissions to assign permissions to people within Teams, with special permissions going to the team managers.

These are the features implemented

• Every member, including managers, can view their team; managers additionally receive team edit/delete, member-profile visibility, and member-management permissions.
• Saving or deleting a membership, including changing its manager role through the admin, immediately recomputes that user's permissions for the team.
• Permission rows are assigned to individual users and are removed with the team or user; deleting a team cannot leave permissions that affect a later team.
• A reversible data migration backfills existing memberships and is safe to run on an empty database.
• Tests verify permission outcomes through Django's permission API and guardian object queries, without inspecting permission tables or calling signal handlers directly.
• The membership model documents that membership changes must not use queryset updates or bulk operations that bypass permission synchronization.

Note: Most of this was AI-generated from a spec that included the above checklist. I have tested the behaviour, and it works as expected, but haven't yet thoroughly checked the implementation (mainly, I haven't looked closely at the tests).

Fixes #810

Type of change

• Documentation (non-breaking change that adds or improves the documentation)
• New feature (non-breaking change which adds functionality)
• Optimization (non-breaking, back-end change that speeds up the code)
• Technical work (non-breaking, change which is work as part of a new feature)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (whatever its nature)

Key checklist

• All tests pass (eg. python -m pytest)
• The documentation builds and looks OK (eg. mkdocs serve)
• Pre-commit hooks run successfully (eg. pre-commit run --all-files)

Further checks

• Code is commented, particularly in hard-to-understand areas
• Tests added or an issue has been opened to tackle that in the future. (Indicate issue here: # (issue))

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!