Agent Skills: optimize-perf

Apply performance improvements with before/after benchmarks. Use when asked to "optimize this", "make it faster", "speed this up", "profile and fix", or when the user wants perf fixes applied (not just reviewed). Runs `review-perf` to find candidates, then for each fix writes a benchmark, applies the change, re-measures, and reverts on regression. Companion to `review-perf` (which only finds issues); distinct from `auto-review-code` (which applies generic fixes without wall-clock measurement).