Add configurable BasePath for subfolder hosting and update frontend base handling

wwwroot/js/api.js

@@ -1,7 +1,15 @@
 const defaultHeaders = { "Content-Type": "application/json" };
 
+const metaBase = document.querySelector('meta[name="app-base"]')?.content || "";
+const autoBase = (() => {
+  const parts = window.location.pathname.split("/").filter(Boolean);
+  return parts.length ? `/${parts[0]}` : "";
+})();
+const basePath = metaBase || autoBase;
+const withBase = (path) => `${basePath}${path}`;
+
 async function request(path, { method = "GET", body, adminKey } = {}) {
-  const res = await fetch(path, {
+  const res = await fetch(withBase(path), {
     method,
     headers: {
       ...defaultHeaders,