fix: filter push events by PR branch to prevent timer reset

When a PR was merged to master, the push event affected the merge timer
calculation for all other open PRs. This happened because getDates()
was fetching all repository events and using the most recent PushEvent
regardless of which branch it targeted.

Now the code filters push events to only include those where payload.ref
matches the PR's head branch (refs/heads/<branch-name>), preventing
merges to master or other branches from resetting unrelated PR timers.

Closes #752

Author: TooAngel

src/helpers/pullRequest.js

@@ -35,7 +35,10 @@ async function getDates(githubClient, pull) {
     return Math.max(new Date(total), latestCommitDate);
   }, new Date('January 1, 1970 00:00:00 UTC'));
 
-  // Get push events
+  // Get push events - filter to only include pushes to this PR's branch
+  // The GitHub Events API returns all repo events, so we must filter by ref
+  // to avoid other branch pushes (like merges to master) affecting this PR's timer
+  const prBranchRef = `refs/heads/${pull.head.ref}`;
   const repoEvents = await githubClient.getBranchEvents(
     pull.head.repo.events_url
   );
@@ -44,6 +47,10 @@ async function getDates(githubClient, pull) {
       if (current.type !== 'PushEvent') {
         return new Date(total);
       }
+      // Only consider push events to this PR's branch
+      if (current.payload?.ref !== prBranchRef) {
+        return new Date(total);
+      }
       return new Date(
         Math.max(
           new Date(total).getTime(),