Add "Ask Simba" option to scheduled messages

When use_agent is enabled, the scheduler runs the message content as a
prompt through the LangChain agent and sends Simba's response instead of
the raw content. Frontend adds an Ask Simba toggle with visual indicator.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

blueprints/scheduled_messages/models.py

@@ -36,6 +36,7 @@ class ScheduledMessage(Model):
     recurrence = fields.CharEnumField(
         enum_type=Recurrence, max_length=20, default=Recurrence.NONE
     )
+    use_agent = fields.BooleanField(default=False)
     error_message = fields.TextField(null=True)
     created_by = fields.ForeignKeyField(
         "models.User", related_name="scheduled_messages"