feat(review): test review controls end to end

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Context

The repo has CodeRabbit-style review options such as quiet inline comments, review profiles, path instructions, exclude paths, unified comments, and pre-merge check guidance. We need a focused maintainer-only pass to verify which options are wired, which are only parsed/documented, and which need implementation before self-hosters rely on them.

Parent: #1680

Requirements

• Inventory every CodeRabbit-style review option currently parsed from .gittensory.yml and private repo config.
• Classify each option as fully wired, partially wired, docs-only, or missing.
• Add end-to-end tests for enabled inline comments, profile selection, path instructions, exclude paths, and pre-merge checks where supported.
• Ensure public output remains sanitized and non-blocking inline comments never turn into change-request reviews.
• Document the safe enablement path for self-host operators.

Deliverables

• Wiring matrix in docs or issue notes.
• Tests covering the supported options and negative paths.
• Follow-up implementation issues for any parsed-but-unused options.
• Troubleshooting notes for inline comment posting failures and diff-line validation.

Acceptance criteria

• Supported options have tests that exercise both enabled and disabled paths.
• Unsupported options are clearly documented as not yet available rather than silently implied.
• No public comment leaks private policy or sensitive review controls.
• No labels beyond maintainer-only.

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2026-07-01 audit: consolidated duplicate #1672 here; canonical config-as-code tracking is #1959.