Add noop safe output guidance to workflow creation prompts

[Copilot]

Agents need to signal successful completion when no action is required. Without explicit guidance, agents may fail silently or appear to have not executed, making it unclear whether the workflow ran at all.

Changes

Added noop safe output guidance to create-agentic-workflow.md in three locations:

• Safe Outputs enumeration - Added noop alongside create-issue, add-comment, and create-pull-request with emphasis on transparency
• Prompt Body instructions - Directs creators to include noop guidance in agent prompts (e.g., "no issues to triage, no PRs to create")
• Template structure - Adds "Safe Outputs" section with explicit noop usage pattern:

## Safe Outputs

When you successfully complete your work:
- If you created/modified resources: Use the appropriate safe output (e.g., `create-issue`, `add-comment`)
- **If there was nothing to be done**: Call the `noop` safe output with a clear message explaining 
  that you completed the analysis but no action was necessary.

Rationale

The noop safe output exists per the safe-outputs specification (Section 5.3) but was undocumented in workflow creation guidance. This creates a transparency gap: workflows that analyze but don't modify (e.g., triage workflows finding no issues, compliance checks passing) need to log completion explicitly.

Both .github/aw/ and pkg/cli/templates/ versions updated identically.

Original prompt

Update the "create-agentic-workflow.md" prompt file to make sure that the agent calls the safe output "noop" when it successfully did his work and THERE WAS NOTHING TO BE DONE. This is important because it shows that the agent was able to work AND that no resulting output needed to be created.

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