整合求解器活动监控与步长回归证据

同步远端 PNL0003 诊断和大采样网格能力，语义合并活动感知的 60 秒真停滞判定与旧后端 15 分钟兼容兜底。

纳管热路径优化、15 单元运行证据、浏览器与 API 报告，并补充北京时间更新日志和遗留问题。

app/simulation/benchmark_regression.py

@@ -1038,9 +1038,18 @@ def runtime_snapshot() -> dict[str, object]:
             "SIMULATION_CAUSAL_COORDINATE_KERNEL": os.getenv(
                 "SIMULATION_CAUSAL_COORDINATE_KERNEL", "1"
             ),
+            "SIMULATION_CAUSAL_DIRECT_SUM_ASSIGNMENTS": os.getenv(
+                "SIMULATION_CAUSAL_DIRECT_SUM_ASSIGNMENTS", "1"
+            ),
+            "SIMULATION_CAUSAL_DIRECT_EQUATION_READERS": os.getenv(
+                "SIMULATION_CAUSAL_DIRECT_EQUATION_READERS", "1"
+            ),
             "SIMULATION_CAUSAL_FAST_PATH": os.getenv(
                 "SIMULATION_CAUSAL_FAST_PATH", "1"
             ),
+            "SIMULATION_MECHANICAL_ATOL_MODE": os.getenv(
+                "SIMULATION_MECHANICAL_ATOL_MODE", "legacy"
+            ),
         },
     }