docs: split fork docs gate repair

[Fearvox]

Summary

• split the docs-gate repair out of PR [audit] mega-run packet; docs repair split to #29 #24 into a narrow branch
• keep only the three files needed to repair the docs(contributing): add fork-as-lab workflow section #7/ci(docs): add markdownlint to docs workflow #12 failure paths
• leave the .planning/mega-run/ audit packet in [audit] mega-run packet; docs repair split to #29 #24 as a separate owner-review artifact

Changed Files

• .github/CONTRIBUTING.md
• .github/workflows/docs.yml
• .markdownlint.json

Why

PR #7 is red on Docs links. PR #12 is red on Docs markdown-lint because its workflow scans the legacy tree too broadly. PR #24 proves the fix direction, but it also carries a large .planning/mega-run/ audit packet. This split keeps the repair lane reviewable and lets #7/#12 be superseded without laundering their failures.

Validation

• git diff --cached --check
• npx --yes markdownlint-cli2 .github/CONTRIBUTING.md
• workflow YAML parse
• relative Markdown link check for .github/CONTRIBUTING.md
• added-line safety scan for local paths, auth/header markers, token patterns, and private-key markers

Supersede Plan

If this draft PR passes remote Docs checks, use it as the clean supersede path for:

• docs(contributing): add fork-as-lab workflow section #7 docs(contributing): add fork-as-lab workflow section
• ci(docs): add markdownlint to docs workflow #12 ci(docs): add markdownlint to docs workflow

Do not mark #7/#12 as healthy; close or comment on them only as superseded after this replacement path is green.

Risks

• Remote Docs checks are still source truth for this PR.
• PR [audit] mega-run packet; docs repair split to #29 #24 should remain draft while the owner decides whether the mega-run audit packet belongs in repo history.
• PR docs(agents): refresh fork-side addendum #9 remains separate and DIRTY; this split does not cover it.

Rollback

Close this draft PR and delete the branch. No upstream writes are part of this PR.

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