docs: add JMeter Agent Skill

[QAInsights]

Summary

• add a vendor-neutral jmeter Agent Skill under extras/skills/ using the open Agent Skills format
• guide users through HTTP/API test-plan design, closed/open workload sizing, and evidence-based dashboard reporting
• include reusable Markdown output templates and six behavior evals
• keep execution under human control: the skill never starts JMeter, sends traffic, embeds secrets, or synthesizes raw JMX XML

Discussion points

• whether extras/skills/jmeter/ is the preferred distribution location
• whether one skill with progressively loaded references is preferable to separate skills
• whether the initial HTTP/API, advisory-only scope is appropriate
• whether agent-facing Markdown should remain narrowly excluded from RAT, following the existing token-conscious treatment of agent documentation

Test plan

• uvx --from skills-ref==0.1.1 agentskills validate extras/skills/jmeter
• parsed evals/evals.json as JSON
• exercised focused evals for missing inputs, workload math, report generation, and execution/secret safety
• git diff --check origin/master...HEAD
• full Gradle verification in CI

Local ./gradlew --quiet rat build :src:dist:distZip was attempted in a clean worktree. Verification progressed past the new skill's RAT findings after adding narrow .ratignore entries, but the existing Windows task :src:dist-check:batchBUG_62847 failed independently of these static files. Interrupted attempts first left its log locked; after removing only the orphaned test processes, a clean retry failed because BUG_62847.csv was not produced. No build controls were bypassed and no unrelated source was changed.

[milamberspace]

Thanks @QAInsights for this skill, seems a good start.

I would like discuss to try to have a complete skill for JMeter, so few questions:

1. Why no scripts (jmx file) generation?
2. Why no execution? (non-gui mode/cli)
3. Add JVM / heap tuning guidance? It complements the workload-sizing section.
4. Add HTML dashboard report generation?
5. Distribution / marketplace install (with JMeter archive as local marketplace) (or publish on some official marketplace)

[QAInsights]

Thanks @milamberspace for checking this PR. Please find my responses inline.

• Why no scripts (jmx file) generation?
  Raw jmx/xml is often gets fragile and even frontier LLMs might break the tree integrity; that's why I built Feather Wand with the agentic tool call approach.

• Why no execution? (non-gui mode/cli)
  I will incorporate these in the PR.

• Add JVM / heap tuning guidance? It complements the workload-sizing section.
  Yes, this also can be added; I just wanted to start with something simple for now; that is why I did not include :)

• Add HTML dashboard report generation?
  Yes, will include this as well.

• Distribution / marketplace install (with JMeter archive as local marketplace) (or publish on some official marketplace)
  Local only for now.