refactor(web): restructure into api/domain/services/worker; capabilities, file domains, video covers

- dissolve core-bridge into api (wire contract), domain (models), services (what the UI
  calls) and worker (everything that runs in the Web Worker, grouped by account, crypto,
  space, files, shares, runtime); regroup features, lib and store by responsibility and
  delete unused components
- the UI only reads backend capabilities (domain/capabilities); one tokenRole picks the
  token, hasCode/isRetryable handle errors; pre-checks that decided permissions on the
  client are gone; tests fail if those rules are reimplemented
- files go straight to the file domain (create, upload, download, delete, commit, cancel);
  the host sees one registration per file; creating a channel allocates a file domain and
  works even when the file service is down
- file panel shows which channel the files belong to and its space usage; unlimited files
  preview in chat; videos get a stored cover; the file service status is shown
- fix: console flooded by Retry-After reads on every upload frame

web/src/features/channel/chat/ChatPane.tsx

@@ -0,0 +1,97 @@
+import { Fragment, useEffect, useRef, useState, type ClipboardEvent, type KeyboardEvent } from 'react';
+import { Button } from '@/ui/Button';
+import { useAccount } from '@/store/account/account';
+import { useWorkspace } from '@/store/space/workspace';
+import type { Item } from '@/domain/types';
+import { formatDate } from '@/lib/text/format';
+import { ChatMessage } from './ChatMessage';
+import styles from './ChatPane.module.css';
+
+interface Props { threadName: string; /** 进入频道时的已读位置:之后别人发的第一条消息前画「上次看到这里」 */ lastSeen?: number; ids: string[]; enabled: boolean; onSend: (text: string) => Promise<void>; onDelete: (id: string) => void; onOpenFile: (id: string) => void; onFiles?: (files: File[]) => void }
+
+const MAX_INPUT_HEIGHT = 160;
+
+export function ChatPane({ threadName, lastSeen, ids, enabled, onSend, onDelete, onOpenFile, onFiles }: Props) {
+  const [text, setText] = useState('');
+  const messages = useRef<HTMLDivElement>(null);
+  const input = useRef<HTMLTextAreaElement>(null);
+  const fileInput = useRef<HTMLInputElement>(null);
+  const byId = useWorkspace((s) => s.byId);
+  const self = useAccount((s) => s.username);
+  const chronological = ids.slice().reverse();
+
+  useEffect(() => { messages.current?.scrollTo({ top: messages.current.scrollHeight }); }, [chronological.length]);
+
+  function fit() {
+    const el = input.current;
+    if (!el) return;
+    el.style.height = 'auto';
+    el.style.height = `${Math.min(el.scrollHeight, MAX_INPUT_HEIGHT)}px`;
+  }
+
+  // 乐观发送:不等后端,先清空输入框,消息立刻画出来;失败由消息行自己显示重试
+  function submit() {
+    const value = text.trim();
+    if (!value || !enabled) return;
+    setText('');
+    if (input.current) input.current.style.height = 'auto';
+    void onSend(value);
+  }
+
+  // 粘贴图片(截图、复制的图片)直接当文件发送;只有文字的粘贴照常进输入框
+  function paste(event: ClipboardEvent<HTMLTextAreaElement>) {
+    if (!onFiles || !enabled) return;
+    const images = [...event.clipboardData.files].filter((file) => file.type.startsWith('image/'));
+    if (!images.length) return;
+    event.preventDefault();
+    const stamp = new Date().toLocaleString('sv').replace(/[: ]/g, '-');
+    onFiles(images.map((file, index) => {
+      // 截图的文件名通常就是 image.png,换成带时间的名字,不然连续发几张分不清
+      const generic = /^image\.\w+$/i.test(file.name) || !file.name;
+      const extension = file.type.split('/')[1]?.replace('jpeg', 'jpg') ?? 'png';
+      return generic ? new File([file], `粘贴的图片 ${stamp}${images.length > 1 ? `-${index + 1}` : ''}.${extension}`, { type: file.type, lastModified: file.lastModified }) : file;
+    }));
+  }
+
+  function keyDown(event: KeyboardEvent<HTMLTextAreaElement>) {
+    if (event.key === 'Enter' && !event.shiftKey && !event.nativeEvent.isComposing) { event.preventDefault(); submit(); }
+  }
+
+  return (
+    <section className={styles.pane} aria-label={`${threadName} 聊天`}>
+      <div className={styles.head}><span className={styles.hash} aria-hidden="true">#</span><strong>{threadName}</strong></div>
+      <div className={styles.messages} ref={messages} aria-live="polite">
+        {chronological.length === 0 ? <p className={styles.empty}>这里是 #{threadName} 的开头。发送消息或文件，成员可以看到你的名称和头像。</p> : null}
+        {(() => {
+          let previous: Item | undefined;
+          let seenShown = false;
+          return chronological.map((id) => {
+            const item = byId[id];
+            if (!item) return null;
+            const dateKey = new Date(item.ts).toDateString();
+            const previousDate = previous ? new Date(previous.ts).toDateString() : undefined;
+            const showDate = dateKey !== previousDate;
+            const sameSender = previous && previous.author?.username === item.author?.username;
+            // 分隔线只画在「别人发的第一条新消息」前,而且前面得有已读的消息,否则没有意义
+            const showSeen = !seenShown && lastSeen !== undefined && item.ts > lastSeen && previous !== undefined && item.localId === undefined && item.author?.username !== self;
+            if (showSeen) seenShown = true;
+            const grouped = Boolean(sameSender && !showDate && !showSeen && item.ts - previous!.ts < 5 * 60_000);
+            previous = item;
+            return <Fragment key={id}>
+              {showDate ? <div className={styles.dateDivider} role="separator"><span>{formatDate(item.ts)}</span></div> : null}
+              {showSeen ? <div className={`${styles.dateDivider} ${styles.seenDivider}`} role="separator"><span>上次看到这里</span></div> : null}
+              <ChatMessage id={id} compact={grouped} onOpenFile={onOpenFile} onDelete={onDelete} />
+            </Fragment>;
+          });
+        })()}
+      </div>
+      <form className={styles.composer} onSubmit={(event) => { event.preventDefault(); submit(); }}>
+        {onFiles ? <><input ref={fileInput} type="file" multiple hidden onChange={(event) => { if (event.target.files?.length) onFiles([...event.target.files]); event.target.value = ''; }} />
+          <Button variant="ghost" icon="plus" label="上传文件到当前频道" disabled={!enabled} onClick={() => fileInput.current?.click()} /></> : null}
+        <textarea ref={input} value={text} disabled={!enabled} rows={1} aria-label="消息内容" placeholder={enabled ? `给 #${threadName} 发消息` : '先创建或加入一个频道'}
+          onChange={(event) => { setText(event.target.value); fit(); }} onKeyDown={keyDown} onPaste={paste} />
+        <Button type="submit" variant="ghost" icon="send" label="发送消息" disabled={!enabled || !text.trim()} />
+      </form>
+    </section>
+  );
+}