feat(config): add review.labeling_rules deterministic label suggestions

[JSONbored]

Add review.labeling_rules — a list of {label, when} entries with deterministic path/title/keyword criteria that SUGGEST (and optionally auto-apply when autoLabelEnabled) labels on a PR. No scoring labels. Empty (default) ⇒ no labels suggested (byte-identical). Decomposed from #1959; complements the existing PR-type labeler.

Deliverables

• Add a LabelingRule type ({ label, whenPaths?, titleContains?, descriptionContains? }) and labelingRules: LabelingRule[] to FocusManifestReviewConfig in src/signals/focus-manifest.ts (mirror the parseReviewPreMergeChecks shape at :703)
• Parse review.labeling_rules with public-safe label strings, deterministic when criteria, and the MAX_PATH_INSTRUCTIONS cap; refuse any scoring/reserved label names
• Evaluate rules deterministically at the review path; apply labels only when repository autoLabelEnabled is set (respect src/settings/pr-type-label.ts wiring), otherwise surface as advisory suggestions
• Wire reviewConfigToJson round-trip + present + EMPTY literals; unit tests for each when criterion, autoLabel on/off arms, cap, invalid entry drop
• Document review.labeling_rules in .gittensory.yml.example

References

• src/signals/focus-manifest.ts:703 (parseReviewPreMergeChecks pattern)
• src/signals/focus-manifest.ts:89 (autoLabelEnabled field key)
• src/settings/pr-type-label.ts
• part of #1959 (epic #1953)

Part of #1959.

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size: M · gittensor:feature

[linear-code]

JSO-2162