Store the depth channel in an analysis result and serve it to the 2D depth view

A replay could draw arrows but not depth, and the recording view said there was
nothing to draw even when a result existed. Depth is now quantised per frame
(14 B empty, 486 B at the worst frame seen), read from the cache by the same
draw path live uses, and the raw-recording note appears only when no result
exists. Format version 2; see apps/studio/docs/replay-analysis.md.

apps/studio/config/locales/zh_CN.json

@@ -190,7 +190,7 @@
     "view_mode_tip": "运行时的图像显示模式",
     "replay_pipeline": "录制视频（原始相机图像）",
     "replay_pipeline_tip": "回放显示的是录制下来的原始相机图像，不含实时箭头叠加；要复核算法请用「视图 → 由视频重算力值」",
-    "replay_raw_note": "录像只保存原始相机图像：这里没有光流/深度可画。要看算法处理结果，请用「由视频重算」",
+    "replay_raw_note": "录像只保存原始相机图像：这里没有光流/深度可画，因为这个录像还没有分析结果。打开录像会自动跑一遍分析，也可以点「由视频重算」手动生成；有结果后本面板就能画箭头和深度图",
     "frame_missing_note": "本帧没有{fields}：这个视图这一帧没有数据可画",
     "field_flow": "光流",
     "field_depth": "深度",
@@ -201,6 +201,7 @@
     "arrow_empty_tip": "运行或预览后在此显示形变箭头图",
     "depth_unavailable": "本帧没有深度数据\n（不是深度为零，也未回退显示普通形变图）",
     "depth_scale": "深度色标 {low} – {high}",
+    "depth_empty": "本帧深度全为 0（{pixels} px 中 0 个非零）：色标低端色是一帧真实的零响应，不是缺数据",
     "arrow_scale": "箭头按位移放大 ×{factor}",
     "arrow_scale_tip": "相对位移的显示放大倍率：箭头由原始采集图像经算法输出，长度按测量位移放大后绘制，上限为网格间距的 0.8 倍；触顶的箭头不再呈现真实倍率。",
     "arrow_pipeline": "原始图像 → 算法输出",