[Fix] View changes falls back during GitHub merge state lag

[roomote-roomote]

​Opened on behalf of @mrubens. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• Resolve associated pull requests even while GitHub's state and merged_at fields still reflect their pre-merge values.
• Keep the conservative identity checks that the pushed commit is associated with the PR, targets the pushed branch, and exactly matches the PR's merge commit SHA.
• Add regression coverage using the observed staging merge commit and strengthen rejection coverage for wrong SHA and wrong-base candidates.

Why this change was made

The staging Merge Announcer linked commit 9d606d9be068 to the compare view even though it is the merge commit for PR #1766. Telemetry shows the staging API handled that webhook on develop-d54aa639, which already contained PR #1866, and emitted no GitHub permission or lookup error. The remaining failure was a consistency race: enrichment silently discarded the associated PR unless GitHub had already changed both lifecycle fields to their terminal values.

Impact

Merge Announcer now selects the PR link during GitHub's post-merge consistency window. Direct pushes, unrelated associations, wrong-base PRs, and merge-SHA mismatches continue using the compare fallback.

[roomote-community]

No code issues found. See task

_{Reviewed e4ec211}