fix: exclude worktree branches from merged-branch cleanup in synch-git

Branches checked out in a worktree are prefixed with `+` in `git branch`
output. Without filtering these, the cleanup step would attempt to delete
them and fail.

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

Author: LeeCampbell

scripts/synch-git.sh

@@ -13,7 +13,7 @@ git fetch upstream --prune
 
 echo ""
 echo "=== Deleting local branches merged into main ==="
-merged=$(git branch --merged main | grep -v '^\*\|main' || true)
+merged=$(git branch --merged main | grep -v '^\*\|^+\|main' || true)
 if [ -n "$merged" ]; then
   echo "$merged" | xargs git branch -d
 else