#37 [Admin Panel] User Management API - Create User Endpoint

Implement POST /api/v1/admin/users endpoint to create new users. **API Specification:** - Endpoint: POST /api/v1/admin/users - Permission Required: manage_users - Request Body: {email, display_name, roles[], is_active, metadata{}} - Response: Created user object with user_id **Requirements:** - Validate email format and uniqueness within tenant - Support assigning multiple roles on creation - Send welcome email (optional flag) - Auto-generate temporary password or send OAuth invite - Log audit event for user creation - Return 409 if email exists, 400 for validation errors **Database:** - Create users table if not exists (migration script) - Store: user_id (UUID), tenant_id, email, display_name, is_active, created_at, created_by, metadata (JSONB) **Testing:** - Test with valid data - Test duplicate email handling - Test permission enforcement - Test multi-role assignment **IMPORTANT:** Implement with ultra attention to details and correctness. **BEFORE CLOSING:** Take screenshot of API response in action. Add comment summarizing implementation.