feat(fase4): add FlowTemplate model and API

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

services/api-gateway/app/models/__init__.py

@@ -4,6 +4,7 @@ from app.models.flow import Flow, FlowSession, TriggerType
 from app.models.queue import Queue, QueueAgent, AssignmentMethod
 from app.models.quick_reply import QuickReply
 from app.models.global_variable import GlobalVariable
+from app.models.flow_template import FlowTemplate
 
 __all__ = [
     "User",
@@ -19,4 +20,5 @@ __all__ = [
     "AssignmentMethod",
     "QuickReply",
     "GlobalVariable",
+    "FlowTemplate",
 ]