fix(router): pass isGroup from adapter through to messaging group creation

The router hardcoded is_group=0 when auto-creating messaging groups,
causing channel mentions to be misclassified as DMs. The Chat SDK
bridge knows which handler fired (onDirectMessage vs onNewMention)
so thread the signal through InboundMessage → InboundEvent → router.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/index.ts

@@ -85,6 +85,7 @@ async function main(): Promise<void> {
             content: JSON.stringify(message.content),
             timestamp: message.timestamp,
             isMention: message.isMention,
+            isGroup: message.isGroup,
           },
         }).catch((err) => {
           log.error('Failed to route inbound message', { channelType: adapter.channelType, err });