fix: register /cancel as a proper command

Previously /cancel was intercepted inside the 'unknown' branch, and the
comparison used the command WITHOUT the leading slash while parseCommand
returns it WITH one ('/cancel') — the check never matched, so /cancel
always fell through to the unknown-command reply, even with a pending
ask/approval.

Now a first-class command (menu included): closes the TG-side
answer/approval channel when one is pending, otherwise reports that
nothing is awaiting a reply.

lib/bridge.js

@@ -107,6 +107,7 @@ export class TelegramBridge {
             { command: 'stop', description: '中止当前正在运行的任务' },
             { command: 'mission', description: '查看任务清单与完成情况' },
             { command: 'new', description: '在当前工作区新开对话并附着' },
+            { command: 'cancel', description: '关闭 TG 端作答/审批（Web 端仍可答）' },
             { command: 'help', description: '显示帮助' },
         ]).then(() => {
             this.ctx.logger.info('dsh-telegram-channel: bot commands registered');
@@ -204,19 +205,20 @@ export class TelegramBridge {
             case 'new':
                 await this.newSessionHere(chatId);
                 return;
-            case 'unknown':
+            case 'cancel': {
                 // /cancel closes the TG-side answer/approval channel; the UI side stays open.
-                if (parsed.command === 'cancel') {
-                    let cancelled = false;
-                    if (this.pendingApprovalsTG.delete(String(chatId)))
-                        cancelled = true;
-                    if (this.pendingAsks.delete(String(chatId)))
-                        cancelled = true;
-                    if (cancelled) {
-                        await this.enqueueNotice(chatId, '已关闭 TG 端作答/审批（该问题仍可在 Web 端回答）');
-                        return;
-                    }
-                }
+                let cancelled = false;
+                if (this.pendingApprovalsTG.delete(String(chatId)))
+                    cancelled = true;
+                if (this.pendingAsks.delete(String(chatId)))
+                    cancelled = true;
+                if (cancelled)
+                    await this.enqueueNotice(chatId, '已关闭 TG 端作答/审批（该问题仍可在 Web 端回答）');
+                else
+                    await this.client.sendMessage(chatId, '当前没有待作答的提问或审批');
+                return;
+            }
+            case 'unknown':
                 await this.client.sendMessage(chatId, MSG.unknown(parsed.command));
                 return;
             case 'plain': {