feat(confidence): report calibrated confidence on every stage and fix

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

skills/confidence/SKILL.md

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+---
+name: confidence
+description: >
+  Report calibrated confidence unprompted. Trigger whenever you stage
+  changes, declare a fix or bundle ready, or summarize completed work the
+  operator may commit or deploy — the operator must never have to ask "how
+  sure are you?". Portable across projects.
+---
+
+Every stage summary, fix report, or ready-to-commit bundle ends with a
+confidence block:
+
+1. **Fix confidence** (percent): probability the change does what it
+   claims. **Break risk** (percent): probability it breaks anything else.
+   Two separate numbers, never one blended figure.
+2. **Evidence**: the strongest proof lines only — what was executed,
+   reproduced, enumerated, or read from authoritative source. Distinguish
+   proven (ran it, saw it) from derived (reasoned statically).
+3. **Residuals**: name exactly what keeps the number below 100 and what
+   would close the gap (live deploy, missing artifact, unexercised path).
+   Never a bare percentage without its residuals.
+
+Calibration rules:
+- Number the claim you verified, not the effort you spent; discount after
+  any error the operator caught in the same area.
+- Distinguish "fixes the observed failure" from "makes the job green" when
+  hidden layers may follow, and give both numbers.
+- Static analysis alone caps at the low nineties; only executed evidence
+  (test, reproduction, live probe) justifies more.