[help wanted] Minimal JMH module (3 benchmarks) + PERFORMANCE.md SLO

[DavidHLP]

Goal (v0.1.0, P1)

Establish a defensible performance story: how much does the protection chain cost?

Scope

• New resicache-bench module (JMH).
• 3 benchmarks: (1) chain pass-through vs Spring-native @Cacheable, (2) per-handler additive cost, (3) SyncLock throughput under concurrency.
• PERFORMANCE.md with SLO numbers measured, not guessed (baseline first, then fill).

Refs

• guide §v0.1.0 (line 293), wiki/modules/observability.md