migration: preserve frontend shell pages and styles

app/frontend/shared/components.js

@@ -0,0 +1,54 @@
+(function exposeSharedComponents(global) {
+  "use strict";
+
+  const ui = global.XiaobaiUI;
+  if (!ui) throw new Error("XiaobaiUI must load before shared components");
+
+  function resolveElement(target, root = document) {
+    if (target instanceof Element) return target;
+    if (typeof target !== "string" || !target) return null;
+    return target.startsWith("#") ? root.querySelector(target) : root.getElementById?.(target);
+  }
+
+  function classNames(...values) {
+    return values.flatMap((value) => String(value || "").split(/\s+/)).filter(Boolean).join(" ");
+  }
+
+  function emptyStateHtml(message, options = {}) {
+    const classes = classNames("empty-state", options.className);
+    const attributes = options.role ? ` role="${ui.escapeHtml(options.role)}"` : "";
+    return `<div class="${ui.escapeHtml(classes)}"${attributes}>${ui.escapeHtml(message)}</div>`;
+  }
+
+  function renderEmptyState(target, message, options = {}) {
+    const element = resolveElement(target, options.root);
+    if (!element) return false;
+    element.innerHTML = emptyStateHtml(message, options);
+    return true;
+  }
+
+  function setText(target, value, options = {}) {
+    const element = resolveElement(target, options.root);
+    if (!element) return false;
+    element.textContent = value == null ? "" : String(value);
+    return true;
+  }
+
+  function renderCollection(target, items, renderItem, options = {}) {
+    const element = resolveElement(target, options.root);
+    if (!element) return 0;
+    const rows = Array.isArray(items) ? items : [];
+    element.innerHTML = rows.length
+      ? rows.map((item, index) => renderItem(item, index)).join("")
+      : emptyStateHtml(options.emptyMessage || "", options.emptyOptions);
+    return rows.length;
+  }
+
+  global.XiaobaiComponents = Object.freeze({
+    classNames,
+    emptyStateHtml,
+    renderCollection,
+    renderEmptyState,
+    setText,
+  });
+})(window);