fix(gsd): skip current milestone in syncWorktreeStateBack to prevent merge conflicts

syncWorktreeStateBack copied all milestone directories including the one
being merged. This caused dirty-tree conflicts when mergeMilestoneToMain
ran because the files already existed from the copy-back.

Now skips the current milestoneId in the sync loop since its files are
already in the milestone branch being merged.

Closes #3641

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/resources/extensions/gsd/auto-worktree.ts

@@ -770,6 +770,9 @@ export function syncWorktreeStateBack(
       .map((d) => d.name);
 
     for (const mid of wtMilestones) {
+      // Skip the current milestone being merged — its files are already in the
+      // milestone branch and would conflict with the squash merge (#3641).
+      if (mid === milestoneId) continue;
       syncMilestoneDir(wtGsd, mainGsd, mid, synced);
     }
   } catch (err) {