fix(gateway/bluebubbles): fall back to data.chats[0].guid when chatGuid missing

BlueBubbles v1.9+ webhook payloads for new-message events do not always
include a top-level chatGuid field on the message data object. Instead,
the chat GUID is nested under data.chats[0].guid.

The adapter currently checks five top-level fallback locations (record and
payload, snake_case and camelCase, plus payload.guid) but never looks
inside the chats array. When none of those top-level fields contain the
GUID, the adapter falls through to using the sender's phone/email as the
session chat ID.

This causes two observable bugs when a user is a participant in both a DM
and a group chat with the bot:

1. DM and group sessions merge. Every message from that user ends up with
   the same session_chat_id (their own address), so the bot cannot
   distinguish which thread the message came from.

2. Outbound routing becomes ambiguous. _resolve_chat_guid() iterates all
   chats and returns the first one where the address appears as a
   participant; group chats typically sort ahead of DMs by activity, so
   replies and cron messages intended for the DM can land in a group.

This was observed in production: a user's morning brief cron delivered to
a group chat with his spouse instead of his DM thread.

The fix adds a single fallback that extracts chat_guid from
record["chats"][0]["guid"] when the top-level fields are empty. The chats
array is included in every new-message webhook payload in BB v1.9.9
(verified against a live server). It is backwards compatible: if a future
BB version starts including chatGuid at the top level, that still wins.

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

gateway/platforms/bluebubbles.py

@@ -835,6 +835,12 @@ class BlueBubblesAdapter(BasePlatformAdapter):
             payload.get("chat_guid"),
             payload.get("guid"),
         )
+        # Fallback: BlueBubbles v1.9+ webhook payloads omit top-level chatGuid;
+        # the chat GUID is nested under data.chats[0].guid instead.
+        if not chat_guid:
+            _chats = record.get("chats") or []
+            if _chats and isinstance(_chats[0], dict):
+                chat_guid = _chats[0].get("guid") or _chats[0].get("chatGuid")
         chat_identifier = self._value(
             record.get("chatIdentifier"),
             record.get("identifier"),