移除旧版 HTML 模板与兼容层，并完善私信、举报、媒体存储与 SEO。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/components/ComposeMessageDialog.tsx

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+import { useState } from 'react';
+import { Button } from '@/components/ui/button';
+import {
+  Dialog,
+  DialogContent,
+  DialogDescription,
+  DialogFooter,
+  DialogHeader,
+  DialogTitle,
+} from '@/components/ui/dialog';
+import { notify } from '@/lib/notify';
+import { api } from '../api/client';
+
+interface Props {
+  open: boolean;
+  onOpenChange: (open: boolean) => void;
+  toUserId: number;
+  toNickname: string;
+  onSent?: () => void;
+}
+
+/** 发送私信对话框（对话式，无需标题） */
+export default function ComposeMessageDialog({
+  open,
+  onOpenChange,
+  toUserId,
+  toNickname,
+  onSent,
+}: Props) {
+  const [content, setContent] = useState('');
+  const [sending, setSending] = useState(false);
+
+  const handleOpenChange = (next: boolean) => {
+    if (!next) setContent('');
+    onOpenChange(next);
+  };
+
+  const submit = async () => {
+    if (!content.trim()) {
+      notify.warning('请填写内容');
+      return;
+    }
+    setSending(true);
+    try {
+      await api.sendMessage({
+        to_user_id: toUserId,
+        content: content.trim(),
+      });
+      notify.success('私信已发送');
+      handleOpenChange(false);
+      onSent?.();
+    } catch (e: unknown) {
+      notify.error(e instanceof Error ? e.message : '发送失败');
+    } finally {
+      setSending(false);
+    }
+  };
+
+  return (
+    <Dialog open={open} onOpenChange={handleOpenChange}>
+      <DialogContent className="sm:max-w-md">
+        <DialogHeader>
+          <DialogTitle>发送私信</DialogTitle>
+          <DialogDescription>发给 {toNickname}</DialogDescription>
+        </DialogHeader>
+        <div className="pm-compose-fields">
+          <label className="pm-field">
+            <span className="sr-only">内容</span>
+            <textarea
+              value={content}
+              onChange={(e) => setContent(e.target.value)}
+              rows={6}
+              maxLength={4000}
+              placeholder="写点什么…"
+              autoFocus
+            />
+          </label>
+        </div>
+        <DialogFooter>
+          <Button variant="outline" onClick={() => handleOpenChange(false)}>取消</Button>
+          <Button loading={sending} onClick={submit}>发送</Button>
+        </DialogFooter>
+      </DialogContent>
+    </Dialog>
+  );
+}