telemetry(smus): Add result when emitting show prompt metric

[ziwikiwi]

Problem

Did not include "Result: Success" in the emitted metric for showing the AGENTS.md prompt, which resulted in a warning when logging the metric.

Solution

Added this missing field.

---

• Treat all work as PUBLIC. Private feature/x branches will not be squash-merged at release time.
• Your code changes must meet the guidelines in CONTRIBUTING.md.
• License: I confirm that my contribution is made under the terms of the Apache 2.0 license.

[amazon-inspector-ohio]

⏳ I'm reviewing this pull request for security vulnerabilities and code quality issues. I'll provide an update when I'm done

[github-actions]

• This pull request modifies code in src/* but no tests were added/updated.
  • Confirm whether tests should be added or ensure the PR description explains why tests are not required.

[amazon-inspector-ohio]

✅ I finished the code review, and didn't find any security or code quality issues.