feat(model-specs): 新增模型规格库——跨 provider 模型参数统一维护（presetDataVersion 54→58）

* feat(model-specs): 新增模型规格库与 schema 契约

- compute/model-specs/：按厂商维护模型内在参数（上下文窗口/最大输出/能力/serviceType/默认温度，不含价签）
- schemas/model-spec.schema.json：Draft-07 契约，spec 允许 null（新文件不影响老客户端 frozen 契约）
- scripts/validate.mjs：pickSchemaKey 纳入 model-specs 校验
- manifest.presetDataVersion 54→55

* feat(model-specs): 新增小米 MiMo 系列模型规格；bump presetDataVersion 55→56

* feat(model-specs): 补全全量模型规格；presetDataVersion 56→57

* feat(model-specs): 新增 releasedAt/retiredAt 时间戳字段；补充 mimo 退役日期

compute/model-specs/xai.json

@@ -0,0 +1,31 @@
+{
+  "description": "xAI Grok 系列模型规格。参数来源：config-center compute/providers/xai.json。Grok 网关命名变体较多（含日期戳/-fast/-reasoning 后缀），主要依赖 family=grok-4 兜底匹配。",
+  "specs": [
+    {
+      "id": "grok-4-1-fast-reasoning",
+      "displayName": "Grok 4.1 Fast",
+      "family": "grok-4",
+      "spec": {
+        "contextWindow": 2000000,
+        "maxOutputTokens": 16384,
+        "capabilities": ["chat", "reasoning", "code", "vision", "tool_use", "fast", "long_context"],
+        "serviceType": ["chat", "reasoning"],
+        "defaultTemperature": 1,
+        "supportsReasoning": true
+      }
+    },
+    {
+      "id": "grok-4.20-0309-reasoning",
+      "displayName": "Grok 4.20",
+      "family": "grok-4",
+      "spec": {
+        "contextWindow": 2000000,
+        "maxOutputTokens": 16384,
+        "capabilities": ["chat", "reasoning", "code", "vision", "tool_use"],
+        "serviceType": ["chat", "reasoning"],
+        "defaultTemperature": 1,
+        "supportsReasoning": true
+      }
+    }
+  ]
+}