fix(board): unwrap API envelope in composables, isolate member profile fetch

app/composables/useBoardChannels.js

@@ -7,7 +7,7 @@ export function useBoardChannels() {
 
   async function fetchChannels() {
     const result = await $fetch('/api/board/channels')
-    channels.value = result || []
+    channels.value = result?.channels || []
     return channels.value
   }
 

app/composables/useBoardPosts.js

@@ -10,7 +10,7 @@ export function useBoardPosts() {
     loading.value = true
     try {
       const result = await $fetch('/api/board/posts', { params })
-      posts.value = result || []
+      posts.value = result?.posts || []
       return posts.value
     } finally {
       loading.value = false