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/scripts/fetch-openapi.js

@@ -0,0 +1,25 @@
+import fs from "fs";
+import path from "path";
+import axios from "axios";
+
+// Single config point
+const config = { schemaUrl: "/api/schema/", baseUrl: "/api/" };
+
+async function main() {
+  const outDir = path.resolve("./src/openapi");
+  const outFile = path.join(outDir, "schema.json");
+  const base = process.env.VITE_API_BASE_URL || "http://localhost:8000";
+  const url = new URL(config.schemaUrl, base).toString();
+
+  console.log(`[openapi] Fetching schema from ${url}`);
+  const res = await axios.get(url, { headers: { Accept: "application/json" } });
+
+  await fs.promises.mkdir(outDir, { recursive: true });
+  await fs.promises.writeFile(outFile, JSON.stringify(res.data, null, 2), "utf8");
+  console.log(`[openapi] Wrote ${outFile}`);
+}
+
+main().catch((err) => {
+  console.error("[openapi] Failed to fetch schema:", err?.message || err);
+  process.exit(1);
+});