[codex] add auditable mutation exclusions

[greenthree]

What changed

• Add mutation.schema_version: 1 with bounded, exact-ID exclusions and stable lint diagnostics.
• Apply exclusions before --max-mutants, and distinguish matched, out-of-scope, and unmatched records.
• Upgrade local mutation evidence to v2 with raw/excluded/effective/selected counts, current Core/compiler identity checks, stale-generation isolation, and atomic publish failure handling.
• Surface exclusion status and reasons in JSON, text, and Markdown reports without duplicate lint diagnostics.
• Update the Skill, README, CLI reference, Schema reference, mutation guide, package inventory, and ignore rules.

Why

Mutation testing can produce equivalent or inapplicable mutants. Authors need an auditable way to record those manual reviews without inflating the execution limit or silently losing stale IDs. Partial-operator runs also need to distinguish an exclusion that is merely outside the current run from one that no longer exists.

This remains advisory evidence. It does not prove correctness and does not become a build hard gate.

Validation

• npm run check: 691 passed, 30 skipped
• npm run pack:check: probhub 221 files, probhub-skill 5 files
• Mutation/config/report targeted tests: 32 passed
• Skill quick validation: passed
• phtest nine-problem Schema v1 lint: passed
• git diff --check: passed
• Two same-model read-only reviews: no remaining blockers