feat(ai): 实现AI模型调用的积分计费功能

- 后端根据请求体中的n参数计算AI调用次数并扣减用户积分
- 添加readAIRequestCount函数解析multipart/form-data和JSON格式的请求体获取调用次数
- 前端Canvas组件中显示预计消耗的积分数量
- 在助手面板、配置节点面板和提示面板中集成积分成本计算和展示
- 优化模型选择器在云端模式下的模型列表显示逻辑
- 添加CreditSymbol组件用于统一积分图标显示
- 实现requestCreditCost函数计算远程调用的积分消耗
- 更新文档中关于积分扣费和模型配置的相关说明

web/src/constant/credits.tsx

@@ -0,0 +1,25 @@
+import type { ComponentProps } from "react";
+import { Zap } from "lucide-react";
+
+export function CreditSymbol({ className, ...props }: ComponentProps<"span">) {
+    return (
+        <span {...props} className={`inline-flex items-center justify-center ${className || ""}`}>
+            <Zap className="size-[1em] fill-current" strokeWidth={2.4} />
+        </span>
+    );
+}
+
+export type ModelCreditCost = {
+    model: string;
+    credits: number;
+};
+
+export function modelCreditCost(modelCosts: ModelCreditCost[] | undefined, model: string) {
+    return modelCosts?.find((item) => item.model === model)?.credits || 0;
+}
+
+export function requestCreditCost(options: { channelMode: string; modelCosts?: ModelCreditCost[]; model: string; count?: string | number }) {
+    if (options.channelMode !== "remote") return 0;
+    const count = Math.max(1, Math.floor(Math.abs(Number(options.count)) || 1));
+    return modelCreditCost(options.modelCosts, options.model) * count;
+}