Add multi-lens-review skill: parallel finder lenses + adversarial voters

.claude/skills/multi-lens-review/SKILL.md

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+---
+name: multi-lens-review
+description: Review a diff, branch, or module with parallel finder agents,
+  each holding ONE lens (reuse, simplification, efficiency, altitude/design,
+  correctness), then adversarially verify each finding with independent
+  voter agents before reporting. Use for pre-merge review, branch audits,
+  or "find problems in X" asks that deserve more than one pass.
+---
+
+# Multi-lens review
+
+One reviewer misses what a different lens catches; one finding presented
+without verification wastes reviewer trust. Structure:
+
+1. **Scope**: resolve the target to a concrete diff or file list
+   (`git diff main...branch`, or the module's files). Paste the scope into
+   every agent prompt; agents do not re-derive it.
+
+2. **Finder fan-out**: one agent per lens, in parallel, each prompted with
+   ONLY its lens:
+   - *reuse*: duplicated logic, existing helpers not used
+   - *simplification*: complexity that a smaller construct removes
+   - *efficiency*: allocation, IO, algorithmic waste on hot paths
+   - *altitude*: wrong layer / API-shape / naming-level concerns
+   - *correctness*: inputs/state that produce wrong results
+
+   Finders return findings as `file:line - claim - why it matters`.
+   Worker model: Sonnet by default; Opus only for correctness on
+   intricate logic.
+
+3. **Adversarial voters**: for each finding, 3 parallel agents prompted to
+   REFUTE it ("prove this is fine or intended; default to refuted if
+   uncertain"). Keep findings with at least 2 non-refutes. Voters:
+   Haiku/Sonnet.
+
+4. **Report**: surviving findings ranked by severity, each with its
+   file:line, the failure scenario, and which lens found it. No fixes
+   unless asked.