leo: warn on NULL source_path in _terminate_pr (Ganymede nit)

If source_path is NULL, the source requeue silently matches nothing.
Log a warning so we catch orphaned terminations in monitoring.

Pentagon-Agent: Leo <294C3CA1-0205-4668-82FA-B984D54F48AD>

lib/evaluate.py

@@ -151,12 +151,14 @@ async def _terminate_pr(conn, pr_number: int, reason: str):
     )
 
     # Tag source for re-extraction with feedback
-    conn.execute(
+    cursor = conn.execute(
         """UPDATE sources SET status = 'needs_reextraction',
            updated_at = datetime('now')
            WHERE path = (SELECT source_path FROM prs WHERE number = ?)""",
         (pr_number,),
     )
+    if cursor.rowcount == 0:
+        logger.warning("PR #%d: no source_path linked — source not requeued for re-extraction", pr_number)
 
     db.audit(conn, "evaluate", "pr_terminated", json.dumps({
         "pr": pr_number, "reason": reason,