feat(compute): 添加 qwen3.8-max-preview 模型 (#66)

- 新增 Qwen3.8-Max Preview 到 dashscope provider 和 model-specs
- 100万上下文，支持视觉理解（serviceType 含 vision）、Agent、推理
- supportsReasoning: true
- 定价：输入 ¥12/M token，输出 ¥36/M token
- presetDataVersion 81 → 82

compute/model-specs/qwen.json

@@ -1,6 +1,22 @@
 {
   "description": "阿里通义千问 Qwen 系列模型规格。参数来源：config-center compute/providers/dashscope.json。",
   "specs": [
+    {
+      "id": "qwen3.8-max-preview",
+      "displayName": "Qwen3.8 Max Preview",
+      "family": "qwen3.8",
+      "match": { "exact": ["qwen3.8-max-preview"], "patterns": ["qwen3.8-max-preview*"] },
+      "spec": {
+        "contextWindow": 1000000,
+        "maxOutputTokens": 65536,
+        "capabilities": ["chat", "reasoning", "code", "multilingual", "tool_use", "long_context", "agent", "vision"],
+        "serviceType": ["chat"],
+        "defaultTemperature": 0.6,
+        "defaultTopP": 0.95,
+        "supportsReasoning": true,
+        "description": "通义千问 Qwen3.8 Max 预览版，100 万上下文，支持视觉理解"
+      }
+    },
     {
       "id": "qwen3.7-max",
       "displayName": "Qwen3.7 Max",