feat(platform): 模型可用性 - 目录附带近24小时成功率与7天趋势

公开目录只统计系统渠道的 create 成败，样本不足或日志不可用时不改变现有可用判断；模型选择器展示当前可用状态和历史成功率。

web/src/services/api/logical-models.ts

@@ -181,6 +181,23 @@ export type PublicChannelModel = {
     displayPrice?: number;
     priceLabel: string;
     available: boolean;
+    availability?: PublicChannelModelAvailability;
+};
+
+export type PublicChannelModelAvailability = {
+    rate24h: number | null;
+    sampleCount24h: number;
+    trend7d: PublicChannelModelAvailabilityDay[];
+    dataState: "ready" | "insufficient" | "no_data";
+    computedAt: string;
+    dataThrough?: string;
+};
+
+export type PublicChannelModelAvailabilityDay = {
+    day: string;
+    rate: number | null;
+    sampleCount: number;
+    dataState: "ready" | "insufficient" | "no_data";
 };
 
 export type PublicChannelModelPriceTier = {