fix(ingest): Add frontmatter missing warning to index-append.py

skills/ingest/scripts/index-append.py

@@ -50,6 +50,10 @@ def main() -> int:
         if fm_open and ln.startswith("last_updated:"):
             lines[i] = f"last_updated: {today}"
 
+    if not fm_open:
+        print("index-append: warning: no frontmatter found, last_updated not bumped",
+              file=sys.stderr)
+
     # 2. Locate the target section [start, end)
     start = None
     for i, ln in enumerate(lines):