feat(web): 增加参数即时估价与显式免费编辑

估价请求统一使用 350ms 防抖、AbortController 和请求序号，区分免费、计算中、价格不可用与失败状态，并展示候选冻结上限。价格未就绪时阻止生产提交。\n\n计价规则编辑器新增显式免费开关和 9 位价格步进。\n\n验证：Web 88 项测试和生产构建通过。

apps/web/src/api.ts

@@ -896,10 +896,12 @@ export async function uploadFileToStorage(
 export async function estimatePricing(
   token: string,
   input: Record<string, unknown>,
+  signal?: AbortSignal,
 ): Promise<GatewayPricingEstimate> {
   return request<GatewayPricingEstimate>('/api/v1/pricing/estimate', {
     body: input,
     method: 'POST',
+    signal,
     token,
   });
 }
@@ -1180,7 +1182,7 @@ export async function deleteFileStorageChannel(token: string, channelId: string)
 
 async function request<T>(
   path: string,
-  options: { token?: string; auth?: boolean; method?: string; body?: unknown; headers?: Record<string, string> } = {},
+  options: { token?: string; auth?: boolean; method?: string; body?: unknown; headers?: Record<string, string>; signal?: AbortSignal } = {},
 ): Promise<T> {
   const headers: Record<string, string> = { ...(options.headers ?? {}) };
   if (options.auth !== false && options.token && options.token !== OIDC_BROWSER_SESSION_CREDENTIAL) {
@@ -1194,6 +1196,7 @@ async function request<T>(
     headers,
     body: options.body === undefined ? undefined : JSON.stringify(options.body),
     credentials: 'include',
+    signal: options.signal,
   });
   if (!response.ok) {
     const body = await response.text();