fix(heartbeat): suppress git-only alerts when rest is ok

Uncommitted files alone are not an actionable heartbeat alert.
Only send a message if there are other findings besides git status.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/heartbeat.py

@@ -109,6 +109,11 @@ def run_heartbeat(config: dict | None = None) -> str:
     if not all_results:
         return "HEARTBEAT_OK"
 
+    # Git uncommitted files alone are not an actionable alert — stay silent
+    non_git = [r for r in all_results if not r.startswith("Git:")]
+    if not non_git:
+        return "HEARTBEAT_OK"
+
     return " | ".join(all_results)