feat(reactions): composer focus after toggle-reaction (Phase 521)

Emit composer-focus-channel when toggle-reaction completes in guild
mode so reaction toggles restore composer autofocus like Discord.

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

index.js

@@ -1074,6 +1074,12 @@ async function dispatchUiMessage (platform, msg, hooks = {}) {
   }
   if (t === 'toggle-reaction') {
     await platform.toggleReaction(msg.messageId, msg.emoji)
+    if (platform.activeChannelId && platform.mode === 'guild') {
+      send({
+        type: 'composer-focus-channel',
+        channelId: platform.activeChannelId
+      })
+    }
     pushState()
     return true
   }