feat: add OpenAI OAuth, strict model overrides, and Gmail pull mode

config/default.yaml

@@ -128,6 +128,16 @@ hooks:
 #     enabled: false
 #     credentials_file: ~/.config/flynn/gmail-credentials.json
 #     token_file: ~/.config/flynn/gmail-token.json
+#
+#     # Optional Pub/Sub delivery
+#     # Push mode: configure a topic and a push subscription that POSTs to /gmail/push
+#     pubsub_topic: projects/your-project/topics/gmail-push
+#     disable_push: false
+#
+#     # Pull mode: no inbound webhook required (requires Application Default Credentials)
+#     pubsub_subscription_id: projects/your-project/subscriptions/gmail-pull
+#     pubsub_pull_interval: "60s"
+#     pubsub_max_messages: 10
 #     watch_labels: [INBOX]
 #     poll_interval: "60s"
 #     message: "New email from {{from}}: {{subject}}\n\n{{snippet}}"