docs: add agent guidance files and templates

.claude/skills/fix-review/SKILL.md

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+---
+description: Fix only accepted findings from a diff review. Use after review-diff returns blockers or warnings that the user accepts.
+disable-model-invocation: true
+---
+
+Fix only the accepted review findings.
+
+Rules:
+
+- Do not rewrite the solution.
+- Do not expand scope.
+- Do not address subjective style comments unless accepted by the user.
+- Preserve the original plan unless the user explicitly approved a change.
+- Add or update tests only when needed to cover the accepted finding.
+- Run relevant verification commands again.
+
+Final report:
+
+## Fixes applied
+
+## Files changed since review
+
+## Commands run
+
+## Remaining risks