chore(skills): add repository-local workflow skills (#2190)

.agents/skills/test-coverage-improver/references/coverage-prioritization.md

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+# Coverage Gap Prioritization Guide
+
+Use this rubric for each uncovered area.
+
+Score = (Criticality × 2) + CoverageDebt + (Volatility × 0.5)
+
+- Criticality:
+  - 5: authz/authn, data-loss, payment/consistency path
+  - 4: state mutation, cache invalidation, scheduling
+  - 3: error handling + fallbacks in user-visible flows
+  - 2: parsing/format conversion paths
+  - 1: logging-only or low-impact utilities
+
+- CoverageDebt:
+  - 0: 0–5 uncovered lines
+  - 1: 6–20 uncovered lines
+  - 2: 21–40 uncovered lines
+  - 3: 41+ uncovered lines
+
+- Volatility:
+  - 1: stable legacy code with few recent edits
+  - 2: changed in last 2 releases
+  - 3: touched in last 30 days or currently in active PR
+
+Sort by score descending, then by business impact.