Fix e2e merge-command assertion broken by the ff-only step

Since #40 the conflict comment's fast-forward step reads `git merge
--ff-only origin/<branch>`, which assert_conflict_comment_merges picks
up with its `^git merge` grep, so the extracted commands never match the
expected conflict merges. Skip the --ff-only line when extracting.

Also trim the new comments in the fan-out push/retarget/delete sequence.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01JHvKryT4QUpHYdNq9YEQxX

Author: claude

tests/test_e2e.sh

@@ -291,7 +291,7 @@ assert_conflict_comment_merges() {
         expected+="git merge $conflict"$'\n'
     done
     expected=${expected%$'\n'}
-    actual=$(echo "$comment" | grep -E '^git merge' | sed 's/ *#.*//' || true)
+    actual=$(echo "$comment" | grep -E '^git merge' | grep -v -- '--ff-only' | sed 's/ *#.*//' || true)
 
     if [[ "$actual" == "$expected" ]]; then
         echo >&2 "✅ Verification Passed: conflict comment lists expected merge command(s)."

update-pr-stack.sh

@@ -311,12 +311,9 @@ main() {
         fi
     done
 
-    # Push the updated heads before retargeting, for the same reasons as the
-    # conflict-resume path: the head already contains TARGET_BRANCH when the
-    # base flips to it, keeping the PR mergeable (GitHub suppresses CI on a PR
-    # that conflicts with its base), and a failed push leaves the PR untouched
-    # on its old base instead of retargeted onto a stale head with nothing to
-    # re-trigger this action.
+    # Push the heads before retargeting: a failed push then leaves each PR
+    # intact on its old base, and the head already contains TARGET_BRANCH when
+    # the base flips to it.
     if [[ "${#UPDATED_TARGETS[@]}" -gt 0 ]]; then
         log_cmd git push origin "${UPDATED_TARGETS[@]}"
     fi
@@ -325,9 +322,8 @@ main() {
         log_cmd gh pr edit "$BRANCH" --base "$TARGET_BRANCH"
     done
 
-    # Delete the merged branch last: deleting a PR's base branch closes the PR,
-    # so every child must be retargeted off it first. Keep it while conflicted
-    # PRs remain so it can be referenced during manual resolution.
+    # Deleting a PR's base branch closes the PR, so this must come after the
+    # retargets. Keep the branch for reference while conflicted PRs remain.
     if [[ "${#CONFLICTED_TARGETS[@]}" -eq 0 ]]; then
         log_cmd git push origin ":$MERGED_BRANCH"
     else