Collaborative signal editing (user groups etc)

[happy-devs]

Summary

This request adds collaborative editing capabilities to signals in draft mode. It introduces user groups and signal collaborator features, allowing multiple users to collaborate on a signal before it's published.

New Features

• Added UserGroup entity model for managing groups of users
• Updated Signal entity with is_draft and collaborators fields
• Created database tables for user groups and signal collaborators
• Added CRUD operations for user groups and group membership
• Implemented methods for managing signal collaborators
• Added permission system to control who can edit a signal
• Added API endpoints for all group and collaborator operations
• Added comprehensive test coverage for new functionality

Bug Fixes

No bug fixes.

Checklist

• [] I have read the contribution guidelines.
• [] My code follows the style guidelines of this project.
• [] I have performed a self-review of my code.
• [] I have commented my code, particularly in hard-to-understand areas.
• [] I have added tests that prove my fix is effective or that my feature works.
• [] I have added required dependencies to requirements.txt
• [] I have updated the documentation (if applicable).

Additional Notes

Database Changes

This PR introduces several new database tables:

• user_groups - For managing groups of users
• user_group_members - For managing group membership
• signal_collaborators - For tracking individual user collaborators
• signal_collaborator_groups - For tracking group collaborators
• Added is_draft column to signals table

A SQL migration script is provided in migrations/signal_collaborators.sql.

Key Architecture Decisions

1. Signals default to draft mode (is_draft = true) to allow collaborative work before publication
2. Collaborators can be individual users or entire groups
3. Permission checks cascade - allows user edit access if:
   • They created the signal
   • They are in the collaborators list
   • They are part of a group in the collaborators list
4. Admin users maintain full access to all signals