fix(v2/telegram): await pairing interceptor work to serialize DB commits

The Telegram pairing interceptor fired DB writes (createMessagingGroup,
upsertUser, grantRole) and the pairing-success confirmation inside an
unawaited `void (async () => {...})()`. Recent changes (0d3326a user
privilege model, c483860 pairing confirmation) widened the work done
inside this closure to include an extra two DB writes and a Telegram
API round-trip, making the race between match and commit reproducible
— a paired message could appear "lost" until a second send.

Change onInbound to optionally return a Promise, await it in the
chat-sdk-bridge dispatch callbacks, and make the pairing interceptor
async so its DB writes + confirmation send complete before the handler
resolves.

Note: the upstream @chat-adapter/telegram SDK itself does not await
processUpdate in its polling loop, so the adapter's getUpdates offset
still advances before our handler resolves. A true restart-safe fix
needs a corresponding change in chat-adapter.

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

src/channels/adapter.ts

@@ -20,7 +20,11 @@ export interface ChannelSetup {
   conversations: ConversationConfig[];
 
   /** Called when an inbound message arrives from the platform. */
-  onInbound(platformId: string, threadId: string | null, message: InboundMessage): void;
+  onInbound(
+    platformId: string,
+    threadId: string | null,
+    message: InboundMessage,
+  ): void | Promise<void>;
 
   /** Called when the adapter discovers metadata about a conversation. */
   onMetadata(platformId: string, name?: string, isGroup?: boolean): void;