fix: properly serialize Pydantic HttpUrl in webhook config

Use model_dump(mode='json') instead of deprecated dict() method to ensure
Pydantic special types (HttpUrl, UUID, etc.) are properly serialized to
JSON-compatible native Python types.

This fixes webhook delivery failures caused by HttpUrl objects remaining
as Pydantic types in the webhook_config dict, which caused JSON
serialization errors and httpx request failures.

Also update mcp requirement to >=1.18.0 for compatibility.

deploy/docker/job.py

@@ -86,7 +86,7 @@ async def crawl_job_enqueue(
 ):
     webhook_config = None
     if payload.webhook_config:
-        webhook_config = payload.webhook_config.dict()
+        webhook_config = payload.webhook_config.model_dump(mode='json')
 
     return await handle_crawl_job(
         _redis,