Integrate PurgeScalingGroup Action with existing GraphQL implementation

[jopemachine]

Objective

Complete Purge action with GraphQL integration and comprehensive tests.

Implementation Details

GraphQL mutation (~25 lines)

• PurgeScalingGroupInput with name: str
• PurgeScalingGroupResult with ok: bool, msg: str
• @privileged_mutation decorator with (UserRole.SUPERADMIN,)
• processors.scaling_group.purge_scaling_group.wait_for_complete() call

Action classes (~20 lines)

• PurgeScalingGroupAction(ScalingGroupAction) with name: str
• PurgeScalingGroupActionResult(BaseActionResult) with name: str

Service method (~15 lines)

• purge_scaling_group() in ScalingGroupService
• Call admin repository's purge_scaling_group_force()
• Return PurgeScalingGroupActionResult

Admin Repository (~60 lines)

• Create AdminScalingGroupRepository class
• Pre-flight validation checks:
  • _check_scaling_group_has_active_sessions(): Fail if active sessions exist
  • _check_scaling_group_has_active_agents(): Fail if active agents exist
• purge_scaling_group_force() method with cleanup sequence
• Use @scaling_group_repository_resilience.apply() decorator
• CASCADE FKs auto-delete: sgroups_for_domains, sgroups_for_groups, sgroups_for_keypairs

Processor registration (~10 lines)

• Add purge_scaling_group: ActionProcessor to ScalingGroupProcessors
• Register in supported_actions()

Unit tests

• test_purge_scaling_group_service.py (~80 lines)
• test_purge_scaling_group_repository.py (~100 lines)
• Edge case tests (not found, active sessions/agents exist, validation) (~60 lines)

Estimated Lines

~370 lines

Dependencies

• Story: PurgeScalingGroup Action - Action Spec
• Reference: Group Purge implementation (services/group/actions/purge_group.py)
• Reference: Domain Purge implementation (domain/admin_repository.py)
• Base: Purger utility from repositories/base/purger.py

Acceptance Criteria

• [ ] GraphQL mutation uses new processor pattern
• [ ] PurgeScalingGroupAction properly defined with name identifier
• [ ] Pre-flight checks validate no active sessions/agents exist
• [ ] CASCADE delete handles many-to-many associations automatically
• [ ] Edge cases tested (scaling group not found, active sessions exist, active agents exist)
• [ ] All unit tests pass
• [ ] @privileged_mutation with SUPERADMIN role applied

JIRA Issue: BA-3518