feat(web): message context menu, recall, and basic multi-select

Right-click a message for 复制/撤回/删除/多选 (README §3.5). 引用/收藏/翻译/
转发 deliberately left out of this pass -- quote and forward need their own
composer-state flows, and there's no confirmed single-message favorite
endpoint yet; a menu item that doesn't work is worse than a smaller correct
menu.

- lib/messages/actions.ts: gates recall to own messages, server-confirmed
  seq (not the SDK's local pending-seq placeholder), and bootstrap's
  message_policy.recall_window_seconds -- scoped to P2P for now, no
  group-admin recall yet.
- lib/api/bootstrap.ts + api/hooks.ts: first GET /bootstrap wiring
  (message_policy, forward limits, etc.), cached indefinitely per session.
- lib/api/messages.ts: recall goes through REST, not native WS -- and
  requires a body `{version, reason}` this backend tracks per-message
  independently of Tinode's own seq (confirmed in
  docs/IM-前后端对接文档.md:1248 and by hitting a live 400
  MALFORMED_REQUEST/version first, since no version field is actually
  delivered anywhere in the WS {data} packet this app reads messages from).
  Defaults to version:1 -- the correct value for any never-before-edited
  message, which covers the common case; a real edit/recall race surfaces
  as a version-conflict error rather than being silently papered over.
- Basic multi-select: enter via the context menu's "多选" (no long-press
  gesture yet), header becomes "已选择 N 条消息"+取消, bottom bar currently
  offers only 删除 (bulk 转发/收藏 wait on those features existing).

Verified end to end: recall correctly withheld past the 120s window and
correctly available within it, the real recall REST call round-trips and
the message disappears locally; multi-select mode enters/exits and
pre-selects the long-pressed/right-clicked message.

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

web/src/features/messages/MessageBubble.tsx

@@ -14,9 +14,13 @@ interface MessageRowProps {
   mine: boolean;
   isGroup: boolean;
   peerName: string;
+  selectMode?: boolean;
+  selected?: boolean;
+  onToggleSelect?: (seq: number) => void;
+  onContextMenu?: (e: React.MouseEvent, msg: StoredMessage) => void;
 }
 
-export function MessageRow({ topic, msg, mine, isGroup, peerName }: MessageRowProps) {
+export function MessageRow({ topic, msg, mine, isGroup, peerName, selectMode, selected, onToggleSelect, onContextMenu }: MessageRowProps) {
   if (isServerDeleted(msg)) {
     return <div className="py-1 text-center text-xs text-text-tertiary-4">此消息已被删除</div>;
   }
@@ -40,32 +44,52 @@ export function MessageRow({ topic, msg, mine, isGroup, peerName }: MessageRowPr
   };
 
   return (
-    <div className={`flex items-end gap-2.5 ${mine ? 'flex-row-reverse' : ''}`}>
-      {!mine ? (
-        <span
-          className={`grid h-9 w-9 flex-none place-items-center rounded-lg text-sm font-medium text-white ${avatarBgClass(msg.from || peerName)}`}
+    <div className="flex items-center gap-2">
+      {selectMode ? (
+        <button
+          type="button"
+          onClick={() => typeof msg.seq === 'number' && onToggleSelect?.(msg.seq)}
+          className={`grid h-5 w-5 flex-none place-items-center rounded-full text-[13px] text-white ${
+            selected ? 'bg-accent' : 'border-[1.5px] border-[#c5cad2]'
+          }`}
         >
-          {avatarLetter(peerName)}
-        </span>
-      ) : (
-        <span className="w-9 flex-none" />
-      )}
-      <div className={`flex max-w-[60%] flex-col gap-1 ${mine ? 'items-end' : 'items-start'}`}>
-        <div
-          className={`px-3.5 py-2.5 text-[15px] leading-[1.55] break-words ${
-            mine ? 'rounded-[12px_4px_12px_12px] bg-bubble-mine' : 'rounded-[4px_12px_12px_12px] bg-white shadow-bubble'
-          } ${isRecalled(msg) ? 'text-text-tertiary-4 italic' : ''}`}
-        >
-          {isRecalled(msg) ? '⚠ 消息已删除' : renderDrafty(msg.content)}
-        </div>
-        {failed ? (
-          <button type="button" onClick={retry} className="flex items-center gap-1 text-xs text-danger-text">
-            <Icon name="error" className="text-[16px]" />
-            发送失败，点击重试
-          </button>
+          {selected ? <Icon name="check" className="text-[14px]" /> : null}
+        </button>
+      ) : null}
+      <div
+        onContextMenu={(e) => {
+          if (selectMode) return;
+          e.preventDefault();
+          onContextMenu?.(e, msg);
+        }}
+        className={`flex flex-1 items-end gap-2.5 ${mine ? 'flex-row-reverse' : ''}`}
+      >
+        {!mine ? (
+          <span
+            className={`grid h-9 w-9 flex-none place-items-center rounded-lg text-sm font-medium text-white ${avatarBgClass(msg.from || peerName)}`}
+          >
+            {avatarLetter(peerName)}
+          </span>
         ) : (
-          <span className="text-[11px] text-text-tertiary-3">{sending ? '发送中…' : statusLabel}</span>
+          <span className="w-9 flex-none" />
         )}
+        <div className={`flex max-w-[60%] flex-col gap-1 ${mine ? 'items-end' : 'items-start'}`}>
+          <div
+            className={`px-3.5 py-2.5 text-[15px] leading-[1.55] break-words ${
+              mine ? 'rounded-[12px_4px_12px_12px] bg-bubble-mine' : 'rounded-[4px_12px_12px_12px] bg-white shadow-bubble'
+            } ${isRecalled(msg) ? 'text-text-tertiary-4 italic' : ''}`}
+          >
+            {isRecalled(msg) ? '⚠ 消息已删除' : renderDrafty(msg.content)}
+          </div>
+          {failed ? (
+            <button type="button" onClick={retry} className="flex items-center gap-1 text-xs text-danger-text">
+              <Icon name="error" className="text-[16px]" />
+              发送失败，点击重试
+            </button>
+          ) : (
+            <span className="text-[11px] text-text-tertiary-3">{sending ? '发送中…' : statusLabel}</span>
+          )}
+        </div>
       </div>
     </div>
   );