feat(pairing): auto-close the QR/link dialog once the device connects

The pairing session is single-use, so it leaving the pending list (polled
every 5s) means it was redeemed — close the dialog and toast success. Armed
only after the pairing has been seen in the pending list, so the stale list
at result-phase open can't blink the dialog shut; expired/cancelled sessions
close it silently. Pending-list polling now preserves the previous list on a
transient fetch failure instead of blanking it (which would also have faked
the redeem signal).

packages/ui/src/lib/i18n/messages/zh-TW.settings.ts

@@ -269,6 +269,7 @@
   'settings.remoteInstances.clientAuth.addDevice.fallback.preferLocal': '在家時優先使用直接連線',
   'settings.remoteInstances.clientAuth.addDevice.create': '建立 QR 代碼',
   'settings.remoteInstances.clientAuth.addDevice.done': '完成',
+  'settings.remoteInstances.clientAuth.addDevice.connectedToast': '裝置已連線。',
   'settings.remoteInstances.clientAuth.pairingUrl': '配對 URL',
   'settings.remoteInstances.clientAuth.createdToken': '已建立 token',
   'settings.remoteInstances.clientAuth.state.loading': '正在載入用戶端 token...',