Function aggregatePrDecisions

Aggregates per-voter decisions into a single summary outcome with a verified/unverified tag (#2250 Child 7).

Tiers, in order:

1. Verified blocker (request_changes, verified=true) — at least one non-error voter declared request_changes AND has at least one VERIFIED finding (all 4 gate checks passed with substantive named_assertion). This is the #2225 verification gate.
2. Soft blocker (request_changes, verified=false) — ≥3 of 5 non-error voters voted request_changes, but none produced a verified finding. The retest in #2241 showed voters reliably flag diff-readable bugs at this rate even without producing the YAML structure (#2245 covers why). Tagged unverified so reviewers apply the verification gate themselves.
3. Approve (verified=true) — all non-error voters approve.
4. Abstain (verified=true) — anything else; conservative default.

Why no "AND has any finding" guard on the soft path: the empirical data in pr-review-experiment-results-v2.md showed voters voting request_changes but emitting 0 findings (verified or otherwise). Adding the finding requirement would zero this path out and reproduce the baseline behavior.