feat(config): add review.tone public-safe free-text brief knob

[JSONbored]

Add review.tone — a bounded, public-safe free-text tone brief that complements the enum review.profile, letting maintainers steer the reviewer's voice (e.g. 'concise, cite line numbers') without full instructions. null (default) ⇒ byte-identical reviewer prompt. Decomposed from #1959.

Deliverables

• Add tone: string | null to FocusManifestReviewConfig in src/signals/focus-manifest.ts, parsed via the existing parsePublicSafeText helper (src/signals/focus-manifest.ts:677) with a length cap
• Fold the tone into the reviewer prompt alongside instructions/profile at resolveReviewPromptOverrides (src/signals/focus-manifest.ts:878) so it inherits the public-safe wrapper
• Wire reviewConfigToJson round-trip + present + EMPTY literals
• Unit tests: set/unset (null ⇒ byte-identical prompt), non-public-safe rejected, over-cap truncation; branch coverage on both arms
• Document review.tone in .gittensory.yml.example, noting it complements review.profile

References

• src/signals/focus-manifest.ts:129 (profile field)
• src/signals/focus-manifest.ts:677 (parsePublicSafeText usage)
• src/signals/focus-manifest.ts:878 (resolveReviewPromptOverrides)
• .gittensory.yml.example
• part of #1959 (epic #1953)

Part of #1959.

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size: S · gittensor:feature

[linear-code]

JSO-2161