feat(web): pagination, quote/reply, favorite, and single-message forward

- ConversationView: infinite-scroll "加载更多" -- scroll-to-40px triggers
  topic.msgHasMoreMessages()+getMessagesPage() to fill exactly the missing
  seq ranges (not naive since/before paging, since server-side deletions can
  punch holes in an otherwise-contiguous range), with scroll position
  preserved across the prepend.
- lib/tinode/send.ts: sendReply() ports the old app's exact quote
  construction (Drafty.replyContent truncates, Drafty.quote wraps with the
  sender's name, Drafty.append inlines the whole quote block ahead of the
  new text -- the receiving side never needs to look up the original
  message). forwardMessage() sends a single message directly to one picked
  target topic (ForwardPickerModal) -- simplified from the old app's
  stage-then-compose flow, trading that nicety for a much smaller dialog.
- lib/messages/drafty.tsx: added the 'QQ' Drafty style-tag case ported
  against the SDK's actual Drafty.quote() output shape (no `key`/`data` of
  its own -- verified by reading tinode.dev.js, not guessed).
- lib/api/messages.ts: favoriteMessages() -- a single message is just a
  one-item batch against POST /v1/im/favorites/batch (confirmed in
  docs/IM-前后端对接文档.md:1935).
- Context menu now shows 引用/复制/收藏/转发/多选/[撤回]/删除 in spec order
  (README §3.5); 翻译 still deliberately absent (no real backend for it,
  confirmed by research).

Verified end to end: sent a real quote reply and confirmed the exact wire
packet (head.reply, QQ fmt span, MN entity) and that it renders correctly
via the new QQ formatter case; favorite POSTed and returned created_count:1;
forward POSTed the expected {head:{forwarded:"topic:seq"}} packet.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/features/messages/ForwardPickerModal.tsx

@@ -0,0 +1,63 @@
+import { useState } from 'react';
+
+import { Icon } from '@/app/Icon';
+import { avatarBgClass, avatarLetter } from '@/lib/avatar';
+import { useChatList } from '@/lib/tinode/hooks';
+
+interface ForwardPickerModalProps {
+  onPick: (targetTopic: string) => void;
+  onClose: () => void;
+}
+
+/**
+ * Simplified single-target contact picker for the message context menu's "转发". The full design
+ * (README §3.6) supports multi-select + a merge/separate-forward toggle for the multi-select bulk
+ * bar's forward action -- this is the smaller single-message version, one tap sends immediately.
+ */
+export function ForwardPickerModal({ onPick, onClose }: ForwardPickerModalProps) {
+  const contacts = useChatList();
+  const [query, setQuery] = useState('');
+  const filtered = contacts.filter((c) => !query.trim() || (c.public?.fn || '').includes(query.trim()));
+
+  return (
+    <div className="fixed inset-0 z-50 flex items-center justify-center bg-[#22262d]/25" onClick={onClose}>
+      <div className="flex h-[480px] w-[420px] flex-col rounded-xl bg-white shadow-modal" onClick={(e) => e.stopPropagation()}>
+        <header className="flex h-14 flex-none items-center justify-between border-b border-list-item px-5">
+          <strong className="text-[15px] font-semibold text-text-heading">转发到</strong>
+          <button type="button" onClick={onClose} className="grid h-8 w-8 place-items-center text-text-tertiary-4">
+            <Icon name="close" />
+          </button>
+        </header>
+        <div className="flex-none px-4 pt-3">
+          <div className="flex h-9 items-center rounded-lg bg-surface-search px-3">
+            <Icon name="search" className="text-[18px] text-text-placeholder-2" />
+            <input
+              autoFocus
+              value={query}
+              onChange={(e) => setQuery(e.target.value)}
+              placeholder="搜索会话或联系人"
+              className="ml-2 w-full bg-transparent text-sm outline-none placeholder:text-text-placeholder-2"
+            />
+          </div>
+        </div>
+        <div className="flex-1 overflow-y-auto px-2 py-2">
+          {filtered.map((c) => (
+            <button
+              key={c.topic}
+              type="button"
+              onClick={() => c.topic && onPick(c.topic)}
+              className="flex w-full items-center gap-3 rounded-lg px-3 py-2 text-left hover:bg-surface-rail"
+            >
+              <span
+                className={`grid h-9 w-9 flex-none place-items-center rounded-lg text-sm font-medium text-white ${avatarBgClass(c.topic || '')}`}
+              >
+                {avatarLetter(c.public?.fn)}
+              </span>
+              <span className="truncate text-sm text-text-body">{c.public?.fn || c.topic}</span>
+            </button>
+          ))}
+        </div>
+      </div>
+    </div>
+  );
+}