tooling: pre-commit hook to forbid new top-level WorkflowStep/AgentTask classes (#6951 AC8) #7048

Gap

While verifying #6951 closure, found AC8 was not implemented:

• Pre-commit hook prevents new top-level WorkflowStep/AgentTask classes (similar to no-new-health-route from refactor(backend): consolidate 12 health check implementations — keep /api/system/health as primary #3333)

The canonical WorkflowTask/WorkflowPlan in autobot_shared.workflow exist (#6951 Phase 1b–3 done), but nothing prevents future contributors from re-introducing the same fragmentation.

Repro

```
$ grep -rn "WorkflowStep|AgentTask" .pre-commit-config.yaml
(empty)
```

Recommended fix

Add a local hook to .pre-commit-config.yaml, modeled on the existing no-new-health-route hook from #3333:

```yaml

• id: no-new-workflow-step-class
  name: Prevent new WorkflowStep/AgentTask top-level classes
  entry: scripts/check_no_new_workflow_step_class.py
  language: python
  files: '.py$'
  exclude: '^(autobot_shared/workflow/|autobot-backend/enhanced_orchestration/types.py|autobot-backend/orchestration/types.py|autobot-backend/orchestration/sub_workflow.py|autobot-backend/workflow_templates/types.py)$'
  ```

The script greps for class (WorkflowStep|AgentTask) definitions outside the allowlist (canonical module + already-existing aliases/subclasses + SubWorkflowStep per AC6).

Acceptance Criteria

• Hook present in .pre-commit-config.yaml and named no-new-workflow-step-class
• Hook script at scripts/check_no_new_workflow_step_class.py (Python, exits non-zero with helpful message)
• Allowlist documents the legitimate exceptions: canonical types + 5 known domain-specializations
• Smoke test: synthesizing a new class WorkflowStep: definition outside allowlist → hook fails

Cross-references

• Parent: refactor: unify 5 duplicate WorkflowStep/Task/Plan definitions + add first-class prompt/tools fields #6951 (workflow type unification)
• Pattern reference: no-new-health-route hook from refactor(backend): consolidate 12 health check implementations — keep /api/system/health as primary #3333