Fix: migrate all remaining main_agent imports to current_app

email, scheduled_messages scheduler, and cron blueprints still imported
main_agent directly from agents. All now use current_app.main_agent so
they read the initialized value set by build_agent() in the lifespan.

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

blueprints/email/__init__.py

@@ -7,7 +7,7 @@ import time
 from collections import defaultdict
 
 import httpx
-from quart import Blueprint, request
+from quart import Blueprint, current_app, request
 
 from blueprints.users.models import User
 from blueprints.conversation.logic import (
@@ -15,7 +15,6 @@ from blueprints.conversation.logic import (
     add_message_to_conversation,
     persist_agent_tool_messages,
 )
-from blueprints.conversation.agents import main_agent
 from blueprints.conversation.models import Speaker
 from blueprints.conversation.prompts import SIMBA_SYSTEM_PROMPT
 from . import models  # noqa: F401 — register Tortoise ORM models
@@ -204,7 +203,7 @@ async def webhook():
         messages_payload.append({"role": "user", "content": body})
 
         logger.info(f"Invoking LangChain agent with {len(messages_payload)} messages")
-        response = await main_agent.ainvoke({"messages": messages_payload})
+        response = await current_app.main_agent.ainvoke({"messages": messages_payload})
         response_text = response.get("messages", [])[-1].content
         await persist_agent_tool_messages(
             conversation, user, response.get("messages", [])