Keep Fly machines always on for inbound webhooks

Set auto_stop_machines='off' and min_machines_running=1 so Postmark
inbound email webhooks are never dropped due to idle machine shutdown.

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

Author: plc

fly.toml

@@ -14,9 +14,9 @@ primary_region = 'sjc'
 [http_service]
   internal_port = 3000
   force_https = true
-  auto_stop_machines = 'stop'
+  auto_stop_machines = 'off'
   auto_start_machines = true
-  min_machines_running = 0
+  min_machines_running = 1
   processes = ['app']
 
 [[vm]]