Change trading-bootcamp primary region from ewr to sjc

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

Author: crthpl

backend/fly.toml

@@ -4,7 +4,7 @@
 #
 
 app = 'trading-bootcamp'
-primary_region = 'ewr'
+primary_region = 'sjc'
 
 [build]
 dockerfile = 'Dockerfile'