feat(review): skip auto-review of docs-only PRs via review.auto_review.skip_docs_only

[JSONbored]

Part of #1954. Add review.auto_review.skip_docs_only (bool): when enabled and EVERY changed file classifies as docs (via classifyChangedFile === "docs" / isDocsFile, src/signals/path-matchers.ts:182,235), skip the AI review. Deterministic path classification, no AI. Default off ⇒ docs PRs reviewed as today. Empty changed-file list ⇒ NOT docs-only (fail-safe = eligible).

Deliverables

• Parse skip_docs_only (bool) in parseReviewConfig (src/signals/focus-manifest.ts:653); serialize in reviewConfigToJson (src/signals/focus-manifest.ts:835)
• Add a docs-only branch to decideReviewEligibility (src/review/review-eligibility.ts): eligible unless every changed path is docs; reuse classifyChangedFile (src/signals/path-matchers.ts:235) — explicitly decide the empty-list case (treat as eligible)
• Thread the PR's changed-file paths into the eligibility call at maybePublishPrPublicSurface (src/queue/processors.ts:4533)
• Unit tests: all-docs ⇒ skip, mixed docs+source ⇒ eligible, empty file list ⇒ eligible, off ⇒ eligible; 97% branch (test the nullish/empty arm)

References

• src/signals/path-matchers.ts:182
• src/signals/path-matchers.ts:235
• src/queue/processors.ts:4533
• #1954

Part of #1954.

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size: S · gittensor:feature

[linear-code]

JSO-2180