feat(studio-3d): 历史回放里的三维面板 —— 由「重算」通道喂它，并标注来源

- What: `VIEW_SHOWS_3D` 加入 `replay`；`app_window` 新增 `_shows_3d()`（可见性与布局共用一个判据）
  与 `_splitter_sizes_for()`（预设表里的 3D 槽是"二维布局"的描述，面板打开时从最宽的面板借
  `DEFAULT_3D_PANE_WIDTH=340`）；`ThreeDPanel` 新增第三个来源标签（实时采集 / 回放：录像不含三维场 /
  重算通道：由录像重算，非记录值）与 `set_source_kind()`；`ThreeDCoordinator.show_rest()` 把参考模型
  放回屏幕并停止主张测量值（重算停止时调用，否则最后一帧会留在屏幕上）；`Mesh3dPanel` 转发这两者，
  并新增"加载中"状态的修正：切换传感器再切回来时若该包已加载，直接显示已就绪的画面而不是一条永远
  不会被替换的"正在加载"。
- Why: 录像里没有三维场（raw_*.mp4 是原始相机图像，`depth.stored=false`，CSV 只有力值），所以纯回放只能
  显示参考模型；但「从视频重算力值」本来就把同一个运行路径指向录像的原始视频，而采集线程上的三维 sink
  早已注册——因此重算一开始面板就会收到真实的形变帧。这两件事必须由界面区分：一个是"没有测量"，
  一个是"当前算法对这段录像会说什么"，把后者当成记录值展示就是另一种 `display_illustrative`。
- Verification: apps/studio 全量通过（test_scene3d_view.py 32 项，含"回放里面板可见且标注正确""重算时
  标注切换""停止重算后清回参考模型""实时视图标为实时"；test_scene3d_coordinator.py 15 项，含 show_rest
  与"停止时在飞的帧不会随后被显示"）；ui_check 570 项 0 失败（新增"已安装包必须被加载并标注来源"）；
  locale_check 0 缺失；仓库内工程包经 validate_scene 全部 ok。
- Not in this change: 逐帧保存展开场/深度（记录格式变更，设计文档明确否掉）；重算通道本身（已存在，本次
  只是把它的帧接到面板上）；示意位移（仍需 SDK lift + 已确认尺度）。

apps/studio/tools/ui_check.py

@@ -2830,23 +2830,67 @@ def main() -> int:
         pane.set_sensor("box")
         check(pane.showing_message, "the 3D pane kept showing a picture for a box sensor")
 
-        # A finger with no package names where the package belongs and how to build one.
+        # A finger *without* any package names where one belongs and how to build it.
+        # The search is stubbed for this check: the application's config directory may
+        # or may not carry a compiled package on the machine running the check, and a
+        # check that only passes without one would fail the first time one is
+        # installed (the positive case is checked just below).
+        import orisys_studio.ui.mesh3d_panel as _panel_module
+
+        real_find = _panel_module.find_package
+        _panel_module.find_package = lambda *a, **k: None
+        try:
+            fresh_missing = _Mesh3dPanel()
+            fresh_missing.set_sensor("finger")
+            diagnostic = fresh_missing.last_diagnostic
+            check(
+                diagnostic is not None and diagnostic.code == "asset_rejected",
+                f"a missing 3D scene was not reported as an asset problem: {diagnostic}",
+            )
+            if diagnostic is not None:
+                check(
+                    "compile_scene.py" in diagnostic.details.get("compile", ""),
+                    "the missing-scene report does not say how to build one",
+                )
+                check(
+                    str(diagnostic.details.get("directory", ""))
+                    in fresh_missing.message.text()
+                    or fresh_missing.message.text().strip() != "",
+                    "the pane does not name the directory it looked in",
+                )
+            fresh_missing.deleteLater()
+        finally:
+            _panel_module.find_package = real_find
+
+        # And when a package *is* installed, the pane must actually load it: this is
+        # the end-to-end check that the search path, the loader and the widget agree.
         pane.set_sensor("finger")
-        diagnostic = pane.last_diagnostic
-        check(
-            diagnostic is not None and diagnostic.code == "asset_rejected",
-            f"a missing 3D scene was not reported as an asset problem: {diagnostic}",
-        )
-        if diagnostic is not None:
+        shipped = _panel_module.find_package("finger")
+        if shipped is not None:
+            view_for_load = pane.ensure_view()
+            pane.set_enabled(True)
+            deadline = time.time() + 15.0
+            while time.time() < deadline:
+                app.processEvents()
+                assets = getattr(view_for_load, "assets", None) if view_for_load else None
+                if assets is not None:
+                    break
+                time.sleep(0.02)
             check(
-                "compile_scene.py" in diagnostic.details.get("compile", ""),
-                "the missing-scene report does not say how to build one",
+                getattr(view_for_load, "assets", None) is not None,
+                f"the installed 3D scene was never loaded: {pane.last_diagnostic}",
             )
             check(
-                str(diagnostic.details.get("directory", "")) in pane.message.text()
-                or pane.message.text().strip(),
-                "the pane does not name the directory it looked in",
+                not pane.showing_message,
+                "the pane is still showing a message although a scene loaded",
             )
+            if view_for_load is not None and view_for_load.panel is not None:
+                source_text = view_for_load.panel.source_label.text()
+                check(source_text.strip() != "", "the pane does not say where the field comes from")
+                check(
+                    "实时" in source_text or "Live" in source_text,
+                    f"the live view does not label its source: {source_text!r}",
+                )
 
         # The pane's controls must fit the width the window reserves for it.
         view = pane.ensure_view()