feat(mcp): get_host groups a host's parts by kind and says what it cut

#5012 "get_host cuts `parts` without saying so"

- The agent's sub-resources come back as mounts (fullest first),
  interfaces and disk_io (busiest first) and temperatures (hottest first),
  each bounded on its own with total, truncated and a `more` that names
  parts_limit and query_metrics.
- Per-core CPU is a summary (count, min/avg/max, three busiest), so 38
  cores no longer push every interface out of the reply.
- New argument parts_limit (default 20, max 200).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/integration/test_mcp_tools.py

@@ -139,7 +139,9 @@ def test_diagnostic_tools_over_a_seeded_fleet(app):
         assert detail["host_id"] == hid
         assert [m["state"] for m in detail["monitors"]] == ["down"]
         assert detail["monitors"][0]["error"] == "timeout"
-        assert detail["agent"]["parts"]["/"]["disk_used_pct"] == 41.0
+        mount = detail["agent"]["mounts"]
+        assert mount["items"][0]["mount"] == "/" and mount["items"][0]["disk_used_pct"] == 41.0
+        assert mount["total"] == 1 and mount["truncated"] is False
         assert [a["rule_id"] for a in detail["active_alerts"]] == [rule_id]
         assert detail["ansible_target"] is None