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/config/locales/en_US.json

@@ -399,6 +399,12 @@
     "state_no_data": "No valid measurement in this frame — showing the surface model",
     "state_suspended": "Suspended (the view is hidden)",
     "state_unavailable": "3D is unavailable",
+    "source_live": "Live acquisition",
+    "source_live_tip": "The picture comes from the data being acquired right now.",
+    "source_replay": "Replay: the recording stores no 3D field",
+    "source_replay_tip": "A recording stores the raw camera image and the forces, not a per-frame deformation field. Turn on “Recompute forces from the video” and this pane will show the deformation recomputed from the recording.",
+    "source_recompute": "Recomputed from the recording — not the recorded values",
+    "source_recompute_tip": "This is what the current algorithm version says about the recorded footage: it is a check on the algorithm, not the measurement that was recorded at the time.",
     "severity_info": "Note",
     "severity_warning": "Warning",
     "severity_error": "Error",

apps/studio/config/locales/zh_CN.json

@@ -399,6 +399,12 @@
     "state_no_data": "本帧没有有效测量 — 显示表面模型",
     "state_suspended": "已挂起（视图被隐藏）",
     "state_unavailable": "三维不可用",
+    "source_live": "实时采集",
+    "source_live_tip": "画面来自此刻正在采集的数据。",
+    "source_replay": "回放：录像不含三维场",
+    "source_replay_tip": "录像只保存原始相机图像与力值，没有逐帧的形变场。开启「从视频重算力值」后，本面板会由录像重算并把形变显示在这里。",
+    "source_recompute": "重算通道：由录像重算，非记录值",
+    "source_recompute_tip": "这是在当前算法版本下对录像重算得到的形变，用于检查算法；它不是当初记录下来的测量值。",
     "severity_info": "提示",
     "severity_warning": "警告",
     "severity_error": "错误",