新增统一力读数会话 ForceSession

把同帧测量、空载归零、模型推断与共用后处理收进一个 SDK 会话，Studio 显示与记录使用同一样本；旧 Sensor 读数接口保持兼容。以 force session 与受影响 SDK 套件、lint 与文档门禁验证，硬件与真实载荷精度未验证。

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CpCfJF6SvonMKmPZhzKZHb

src/orisys/calibration_context.py

@@ -34,6 +34,15 @@ class CalibrationContext(dict):
         identity["tracker"]["hhd_downsample"] = downsample
         return _feature_signature(identity)
 
+    @property
+    def actual_downsample(self) -> int:
+        """The HHD downsample this runtime context was actually built with."""
+        raw = self.get("hhd_downsample", 1)
+        try:
+            return max(1, int(raw)) if raw is not None else 1
+        except (TypeError, ValueError):
+            return 1
+
 
 def sha256_file(path) -> str:
     return hashlib.sha256(Path(path).read_bytes()).hexdigest()