docs(skills): REPL probes for objects created and destroyed at runtime

[devin-ai-integration]

What and why

Adds a section to .agents/skills/testing-sysml-repl/SKILL.md on observing objects a run creates with new and ends with destroy (the runtime behavior of #468) through the REPL. It records the three things that are not obvious from the command help: %instantiate already runs the definition's performed classifier actions, so a detached %action never shows the objects they created; %instances lists session roots only, so runtime-created nested objects are read through their holder (%features #1, %eval in #1 : size(all P::Car), which also counts declared singleton parts); and a destroyed object's lifetime note appears under the alias holding it, with reads through it printing the error text rather than exposing error identity.

Documentation only; independent of #468 to merge, though the probes only produce the described output once it has landed.

How it was verified

The probes were run against bin/sysml built from #468 on both lifecycle conformance fixtures.

Checklist

• make test and make lint pass locally
• Tests added or updated for the change (docs only)
• Documentation extended where it already covers the surface (see CONTRIBUTING.md)
• Changelog entry added (skill files are not user-facing; none needed)
• baselines regenerated and make docs-counts run if a gate count moved (none moved)
• No internal work-item labels (waves, slices, F4, K5) in the body, docs, or changelog

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.