feat(corrections): absorb retro codify and /review:audit-enforceability into /corrections:codify and remove them #11121

Refs: #7573

Agent Brief

Type: Feature
Summary: /corrections:codify absorbs retro's codify mode and /review:audit-enforceability; both are removed and every reference moves to codify. This is the parent's absorb-and-remove slice.

Current behavior:

• plugins/corrections/skills/codify/SKILL.md "Boundary" says: "It does not run the retro codify mode, /review:audit-enforceability or style; those keep their own counters until a later slice absorbs them." It also says it does not read review comments from pull requests, and its ## Next routes finding-shaped checks to /review:audit-enforceability.
• plugins/review/skills/audit-enforceability/ still exists. It maps each finding in a review findings file to the cheapest deterministic check.
• plugins/session-flow/skills/retro/ still has a codify [reviews] mode (context/codify.md, scripts/fetch-review-comments.sh) that mines merged PR review comments.
• rg -n 'review:audit-enforceability|retro codify' plugins docs --glob '!**/CHANGELOG.md' --glob '!.changes/**' prints about 140 lines across about 60 files on main.

Desired behavior:

• Codify takes the two inputs it lacks, so the removals lose nothing: a review findings file (what audit-enforceability reads), and PR review comments as a counting source, including the author's own after merge (what retro codify reviews reads).
• plugins/review/skills/audit-enforceability/ and retro's codify mode are removed, with their probes, evals, schema keys, config entries and README rows.
• Every reference moves to /corrections:codify. In docs/upstream/ records and in corrections' own files, reword the reference to the current name rather than deleting the record.

Done when

• rg -n 'review:audit-enforceability|retro codify' plugins docs --glob '!**/CHANGELOG.md' --glob '!.changes/**' prints nothing.
• plugins/review/skills/audit-enforceability/ does not exist, and retro's argument hint has no codify mode.
• Codify has eval cases for a findings-file input and a PR-review-comment source, and each removed skill's or mode's eval cases are ported to codify with before/after results in the PR, showing no loss.
• bash plugins/skill-quality/scripts/check-skill.sh --require-evals plugins/corrections/skills exits 0, and so does check-skill.sh for plugins/review/skills and plugins/session-flow/skills.
• scripts/check-changelog-fragments.sh passes with fragments for corrections, review and session-flow.

Out of scope:

• audit-sessions style (also absorbed per the parent): a separate slice.
• Chat and meeting sources (wait for communication).