ci(review): align zero-finding advisor recommendation with merge gate

[apurvvkumaria]

Problem

The canonical maintainer gate accepts only an exact-head PR Review Advisor recommendation of merge_as_is, but the advisor currently emits info_only for high-confidence reviews with zero blockers, zero warnings, and zero suggestions. This leaves otherwise approved, green PRs fail-closed even though the advisor ledger explicitly says no actionable findings remain.

Observed on PRs #7208, #7492, and #7519.

Expected behavior

• merge_as_is means the advisor found no actionable code-review findings; it does not approve the PR or replace human review.
• info_only remains reserved for skipped, unavailable, or genuinely low-confidence/incomplete advisor results.
• Normalization rejects or repairs internally inconsistent zero-finding, high-confidence info_only output.
• Regression tests cover the recommendation mapping and retain fail-closed behavior for unavailable/low-confidence reviews.

Acceptance criteria

• The advisor prompt defines recommendation semantics without implying merge authority.
• A completed high-confidence review with no findings normalizes to merge_as_is.
• Unavailable or incomplete reviews continue to normalize to info_only and fail the maintainer gate.
• Existing advisor and merge-gate tests pass.