support standalone (.shr) activity download via form version

Branch download by the card form 'version' field: standalone packs a flat .shr (no xbot_robot/xbot_extensions, no internal deps), private keeps the current .bot. Also enable kaniko layer cache to skip pip install on code-only builds.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/task.py

@@ -369,5 +369,7 @@ def process_new_robot(app_id, app_secret, action_data):
 
 
 @shared_task(include_result=False)
-def process_push_xbot_activity_bot(activity_code, open_id, open_message_id):
-    push_xbot_activity_bot(activity_code, open_id, open_message_id)
+def process_push_xbot_activity_bot(
+    activity_code, open_id, open_message_id, package_type="private"
+):
+    push_xbot_activity_bot(activity_code, open_id, open_message_id, package_type)