Perf Enablement: Expand self-service-performance-testing skill to cover all tools

What

Expand the self-service-performance-testing skill (v0.2.0) to cover all primary performance tools with no gaps vs. the handbook tool list.

Why

The central skill is the primary mechanism developers and agents use to get self-service performance guidance. If it has gaps — tools that exist in the handbook but aren't covered — developers following the skill's guidance will miss valid options. Closing those gaps makes the skill trustworthy as a complete reference, not just a partial one.

Approach

1. Audit the handbook tool list against current skill coverage — identify gaps
2. Write missing sections (one per uncovered tool)
3. Validate against the eval suite (see eval baseline issue)
4. Submit MR to gitlab-org/ai/skills

Done when

Central skill covers 100% of handbook-listed tools, MR merged.