feat(ui-flow): wire archive-thread IPC with composer focus

Emit thread-archive-result after archive/unarchive so the UI can toast and
refocus the composer on the parent channel.

Co-authored-by: Cursor <[email protected]>

index.js

@@ -1288,7 +1288,21 @@ async function dispatchUiMessage (platform, msg, hooks = {}) {
     return true
   }
   if (t === 'archive-thread') {
-    await platform.archiveThread(msg.threadId, msg.archived !== false)
+    const archived = msg.archived !== false
+    const merged = await platform.archiveThread(msg.threadId, archived)
+    if (platform.mode === 'guild' && platform.activeChannelId) {
+      send({
+        type: 'composer-focus-channel',
+        channelId: platform.activeChannelId
+      })
+    }
+    send({
+      type: 'thread-archive-result',
+      threadId: msg.threadId,
+      archived,
+      channelName: merged?.name || null,
+      compacted: archived
+    })
     pushState()
     return true
   }