fix(web): guard empty channel list in watch to prevent crash

The immediate watcher on configuredChannels accessed list[0].meta.type
without checking if the list was empty, causing a TypeError on initial
mount before data loaded. This crashed the component during setup and
corrupted KeepAlive state, making all bot detail tabs unresponsive.

Made-with: Cursor

apps/web/src/pages/bots/components/bot-channels.vue

@@ -201,6 +201,8 @@ const selectedItem = computed(() =>
 )
 
 watch(configuredChannels, (list) => {
+  if (list.length === 0) return
+
   const first = list[0]
   if (first && !selectedType.value) {
     selectedType.value = first.meta.type ?? null