refactor(api): unify /api contract across frontend, nginx, and backend

frontend/src/api/http.ts

@@ -1,10 +1,10 @@
-import { ApiError, toApiError } from "./errors";
+import { ApiError, isStructuredApiErrorPayload, toApiError } from "./errors";
 
-const API_BASE_URL = (import.meta.env.VITE_API_BASE_URL as string | undefined)?.trim() || "http://localhost:3001";
+const API_ROOT = "/api";
 
 function buildUrl(path: string): string {
   const normalizedPath = path.startsWith("/") ? path : `/${path}`;
-  return `${API_BASE_URL}${normalizedPath}`;
+  return `${API_ROOT}${normalizedPath}`;
 }
 
 async function parseResponseBody(response: Response): Promise<unknown> {
@@ -36,6 +36,14 @@ async function parseResponseBody(response: Response): Promise<unknown> {
 
 const GATEWAY_RETRY_STATUSES = new Set([502, 503, 504]);
 
+/** Повтор при «пустом» 404: часто бывает при нескольких инстансах/прокси до полного деплоя. */
+function shouldRetryIdempotentError(status: number, payload: unknown): boolean {
+  if (GATEWAY_RETRY_STATUSES.has(status)) {
+    return true;
+  }
+  return status === 404 && !isStructuredApiErrorPayload(payload);
+}
+
 function delay(ms: number): Promise<void> {
   return new Promise((resolve) => {
     setTimeout(resolve, ms);
@@ -69,7 +77,7 @@ export async function requestJson<T>(path: string, init?: RequestInit): Promise<
       const payload = await parseResponseBody(response);
 
       if (!response.ok) {
-        const retryable = idempotent && GATEWAY_RETRY_STATUSES.has(response.status) && attempt < maxAttempts;
+        const retryable = idempotent && attempt < maxAttempts && shouldRetryIdempotentError(response.status, payload);
         if (retryable) {
           await delay(80 * attempt);
           continue;