fix: 工具广场统一18000端口 + 去除电量限制 + bot头像更新

nginx反代(tools-nginx.conf)：
- 10个工具统一通过18000端口路径分发
- 解决/static/冲突（Lama精确匹配，其余给LibreTranslate）
- 解决/api/冲突（PDF用sub_filter改为/pdf-api/，/api/给imgcompress）
- Overleaf兜底处理所有未匹配的绝对路径
- 前端工具卡片统一走18000端口+路径

后端：
- 去除对话电量限制（validateUser中的num扣减逻辑）

前端：
- bot头像更新为战知logo（蓝底白字）
- LaTeX公式编辑器"复制为图片"改为"下载为图片"（解决跨域问题）

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/latex-editor/index.html

@@ -67,7 +67,7 @@
     <div class="symbols" id="symbolBar"></div>
     <div class="actions">
       <button class="btn-primary" onclick="copyLatex()">复制公式</button>
-      <button class="btn-secondary" onclick="copyImg()">复制为图片</button>
+      <button class="btn-secondary" onclick="downloadImg()">下载为图片</button>
       <button class="btn-secondary" onclick="document.getElementById('input').value='';render()">清空</button>
     </div>
     <div class="templates">
@@ -121,23 +121,26 @@ function copyLatex() {
   navigator.clipboard.writeText(document.getElementById('input').value);
   showToast('公式已复制！');
 }
-function copyImg() {
+function downloadImg() {
   const el = document.getElementById('preview');
-  const svg = el.querySelector('svg') || el.querySelector('.katex');
-  if (!svg) return;
-  const canvas = document.createElement('canvas');
-  const ctx = canvas.getContext('2d');
-  const data = new XMLSerializer().serializeToString(el);
-  const img = new Image();
-  const blob = new Blob(['<svg xmlns="http://www.w3.org/2000/svg" width="'+el.scrollWidth+'" height="'+el.scrollHeight+'"><foreignObject width="100%" height="100%"><div xmlns="http://www.w3.org/1999/xhtml" style="background:#fff;padding:20px">'+el.innerHTML+'</div></foreignObject></svg>'], {type:'image/svg+xml'});
-  const url = URL.createObjectURL(blob);
-  img.onload = () => {
-    canvas.width = img.width * 2; canvas.height = img.height * 2;
-    ctx.scale(2,2); ctx.drawImage(img, 0, 0);
-    canvas.toBlob(b => { navigator.clipboard.write([new ClipboardItem({'image/png': b})]); showToast('图片已复制！'); });
-    URL.revokeObjectURL(url);
-  };
-  img.src = url;
+  if (!el.querySelector('.katex')) { showToast('请先输入公式'); return; }
+  // 直接用 KaTeX 的 mathml/svg 渲染结果导出为 SVG 文件下载
+  const w = el.scrollWidth + 40, h = el.scrollHeight + 40;
+  const svgStr = `<svg xmlns="http://www.w3.org/2000/svg" width="${w}" height="${h}">
+    <rect width="100%" height="100%" fill="white"/>
+    <foreignObject width="100%" height="100%">
+      <div xmlns="http://www.w3.org/1999/xhtml" style="display:flex;align-items:center;justify-content:center;width:${w}px;height:${h}px;font-size:24px">
+        ${el.innerHTML}
+      </div>
+    </foreignObject>
+  </svg>`;
+  const blob = new Blob([svgStr], {type: 'image/svg+xml'});
+  const a = document.createElement('a');
+  a.href = URL.createObjectURL(blob);
+  a.download = 'formula.svg';
+  a.click();
+  URL.revokeObjectURL(a.href);
+  showToast('图片已下载！');
 }
 function showToast(msg) {
   const t = document.getElementById('toast');