fix(infra): increase API Gateway HTTP API timeout to 30s max

The default timeout was 29s which caused 503 Service Unavailable errors
for long-running LLM calls. Set to maximum allowed 30 seconds.

Author: mottych

coaching/pulumi/__main__.py

@@ -260,6 +260,7 @@
     integration_type="AWS_PROXY",
     integration_uri=coaching_lambda.arn,
     payload_format_version="2.0",
+    timeout_millis=30000,  # Max 30 seconds for HTTP API (API Gateway limit)
 )
 
 aws.apigatewayv2.Route(