缩略图二分定位 + 邻域采样

B. 二分定位 + 邻域采样（我推荐）
把配置的语义从"这就是要生成的 10 档"改成"允许搜索的参数梯度"（比如分辨率梯度、帧率梯度、质量梯度三张表）。运行时：
1. 用每个组合只编 2 帧的方式粗估体积（很便宜）；
2. 靠单调性做二分，几轮就找到"体积刚好不超过目标"的参数点；
3. 在这个点周围取 10 个组合（略高、略低各几个），完整生成。
成本大概是十几次估算编码 + 10 档完整编码，和现在基本持平甚至更省（估算只编 2 帧）。效果是候选真正围绕你输入的目标分布——比如你填 30 KB，出来的就是 22、26、29、31、35 KB 这种，而不是 5 KB 和 300 KB 各一个。
代价是你现在这套配置格式要推翻重做——从"精确档位表"变成"参数范围表"

release/UNIVERSAL_SpineViewer/_locales/en.json

@@ -36,6 +36,13 @@
         "animatedCompressing": "Compressing animated thumbnail {current}/{total}…",
         "animatedWebpUnavailable": "This environment cannot encode WebP. Choose APNG instead.",
         "animatedCannotFit": "The animation cannot be reduced to {target} KB (minimum about {actual} KB). Increase the limit or shorten the frame range.",
+        "animatedPickTitle": "Pick a thumbnail",
+        "animatedPickHint": "Every result keeps a 400×400 canvas; the label shows detail resolution@fps/quality/file size. Select one and press Confirm to replace the thumbnail, or cancel to discard them all.",
+        "animatedPickConfirm": "Confirm",
+        "animatedPriority": "Priority",
+        "priorityResolution": "Resolution first",
+        "priorityFramerate": "Frame rate first",
+        "priorityBalanced": "Alternate resolution and frame rate",
         "qualityLow": "Low",
         "qualityMedium": "Medium",
         "qualityHigh": "High",