mcp/server: log ssh failures so silent empties are debuggable

mcp/server.py

@@ -99,10 +99,17 @@ def _run_via_hubris(remote_host: str, cmd: list[str],
         f"{SSH_USER}@{HUBRIS_HOST}",
         joined,
     ]
-    return subprocess.run(
+    proc = subprocess.run(
         ssh_args, capture_output=True, text=True,
         timeout=timeout or SSH_TIMEOUT * 3,
     )
+    if proc.returncode != 0:
+        import logging as _l
+        _l.getLogger("homelab-mcp").warning(
+            "ssh failed rc=%s host=%s cmd=%r stderr=%r",
+            proc.returncode, remote_host, joined, proc.stderr.strip(),
+        )
+    return proc
 
 
 def _service_to_host(service: str) -> str: