Summary

Implements atomic single and batch member management endpoints to eliminate race conditions when multiple automations add/remove project members simultaneously. The existing set_members endpoint required passing an authoritative list of all members, creating race conditions in concurrent scenarios.

This PR enhances the member management system to support both single-user and batch operations through the same endpoints, providing flexibility for different use cases while maintaining backwards compatibility.

Fixes #2684 (parent ticket #2742)

Changes Made

• Enhanced AddProjectMemberRequest to accept single member or array of members
• Enhanced RemoveProjectMemberRequest to accept single username or array of usernames
• Implemented add_project_members() and remove_project_members() service functions supporting both single and batch operations
• Enhanced POST /api/projects/{project_name}/add_member endpoint for single/batch operations
• Enhanced POST /api/projects/{project_name}/remove_member endpoint for single/batch operations
• Extended ProjectsAPIClient with backwards-compatible methods and new batch methods
• Comprehensive permission controls (managers/admins only, global admin privileges) for all operations
• Support for username or email lookup in both single and batch modes
• Protection against removing all project admins
• Atomic database operations eliminating read-modify-write patterns
• Comprehensive test suite covering single, batch, and edge case scenarios

API Usage

Add a single member
POST /api/projects/my-project/add_member
Body:

{
  "members": {
    "username": "john@example.com",
    "project_role": "user"
  }
}

Add multiple members (batch)
POST /api/projects/my-project/add_member
Body:

{
  "members": [
    {"username": "john@example.com", "project_role": "user"},
    {"username": "jane_doe", "project_role": "manager"},
    {"username": "alice", "project_role": "user"}
  ]
}

Remove a single member
POST /api/projects/my-project/remove_member
Body:

{
  "usernames": "john_doe"
}

Remove multiple members (batch)
POST /api/projects/my-project/remove_member
Body:

{
  "usernames": ["john_doe", "jane@example.com", "alice"]
}

Update existing member role (via add_member)
POST /api/projects/my-project/add_member
Body:

{
  "members": {
    "username": "jane",
    "project_role": "admin"
  }
}

Race Condition Fix

Previously, concurrent automations had to read and rewrite the entire project member list using the set_members endpoint, which led to race conditions and unintended overwrites. This PR introduces atomic add_member and remove_member operations that support both single and batch operations, allowing changes to apply independently and safely—even when triggered simultaneously.