Add choices API endpoint and OpenAPI client setup

Introduces a new /api/choices/ endpoint for fetching model choices with multilingual labels. Updates Django models to use 'cz#' prefix for Czech labels. Adds OpenAPI client generation via orval, refactors frontend API structure, and provides documentation and helper scripts for dynamic choices and OpenAPI usage.

frontend/src/api/privateClient.ts

@@ -0,0 +1,27 @@
+import axios from "axios";
+
+// použij tohle pro API vyžadující autentizaci
+export const privateApi = axios.create({
+  baseURL: "/api/",
+  withCredentials: true, // potřebuje HttpOnly cookies
+});
+
+privateApi.interceptors.response.use(
+  (res) => res,
+  async (error) => {
+    const original = error.config;
+
+    if (error.response?.status === 401 && !original._retry) {
+      original._retry = true;
+
+      try {
+        await privateApi.post("/auth/refresh/");
+        return privateApi(original);
+      } catch {
+        // optional: logout
+      }
+    }
+
+    return Promise.reject(error);
+  }
+);