fix: restore KaTeX assets and deployment checks

backend/static/js/app.js

@@ -1060,15 +1060,40 @@ function switchTool(tool) {
   window.HuluToolbox?.activate(tool);
 }
 
+function normalizeLatexSource(source) {
+  let normalized = String(source || "").trim();
+  if (normalized.startsWith("$$") && normalized.endsWith("$$")) {
+    normalized = normalized.slice(2, -2).trim();
+  } else if (normalized.startsWith("\\[") && normalized.endsWith("\\]")) {
+    normalized = normalized.slice(2, -2).trim();
+  } else if (normalized.startsWith("$") && normalized.endsWith("$")) {
+    normalized = normalized.slice(1, -1).trim();
+  }
+  return normalized.replace(/\\\\(?=[A-Za-z,;:!])/g, "\\");
+}
+
 function renderLatexPreview(source) {
   const target = $("#latex-preview");
   target.replaceChildren();
-  if (!source.trim()) return;
-  if (typeof katex === "undefined") { target.textContent = source; return; }
+  target.classList.remove("latex-preview-error");
+  const normalized = normalizeLatexSource(source);
+  if (!normalized) return;
+  if (typeof globalThis.katex?.render !== "function") {
+    target.classList.add("latex-preview-error");
+    target.textContent = "公式渲染组件加载失败，请刷新页面后重试。";
+    return;
+  }
   try {
-    katex.render(source, target, { throwOnError: false, displayMode: true });
-  } catch {
-    target.textContent = source;
+    globalThis.katex.render(normalized, target, {
+      displayMode: true,
+      throwOnError: true,
+      trust: false,
+      maxExpand: 500,
+      maxSize: 20,
+    });
+  } catch (error) {
+    target.classList.add("latex-preview-error");
+    target.textContent = `公式语法错误：${error.message}`;
   }
 }
 
@@ -1077,7 +1102,10 @@ async function saveFormula() {
   try {
     await api("latex/documents/", {
       method: "POST",
-      body: { title: `公式 ${new Date().toLocaleString()}`, source: $("#latex-source").value },
+      body: {
+        title: `公式 ${new Date().toLocaleString()}`,
+        source: normalizeLatexSource($("#latex-source").value),
+      },
     });
     showToast("公式及首个版本已保存");
   } catch (error) {