fix: guard notification senders when matchedRuleIds are omitted

[baires]

What changed

• normalize evaluation payloads from the API before the notification senders run
• default missing reviewer arrays to empty arrays
• derive matchedRuleIds from evidence[].ruleId when the API omits the explicit field
• add a regression test covering the partial evaluation shape seen from the live backend

Why

The live MergeWire backend returned evaluation evidence and reviewers, but omitted matchedRuleIds for the demo-repo validation PRs. The action successfully posted PR comments and requested reviewers, then crashed in the Slack sender on matchedRuleIds.length, which prevented Slack and webhook delivery.

Validation

• npm test
• npm run typecheck
• npm run release

[gemini-code-assist]

Code Review

This pull request introduces a normalizeEvaluation function to the API client to ensure that evaluation results have consistent array structures for evidence, matched rule IDs, and requested reviewers. It also includes logic to derive matchedRuleIds from the evidence list if the API omits them, along with a new test case to verify this functionality. Feedback was provided to ensure that matchedRuleIds contains unique values by using a Set, preventing duplicates that might arise from multiple evidence items sharing the same rule ID.