Match master's Dockerfile - use Puma instead of Thruster

The PR review app should use the same server as production to accurately
test early hints behavior. Master uses Puma directly, not Thruster.

Puma supports HTTP/1.1 103 Early Hints as documented in Shakapacker.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: justin808

.controlplane/Dockerfile

@@ -79,5 +79,4 @@ ENTRYPOINT ["./.controlplane/entrypoint.sh"]
 
 # Default args to pass to the entry point that can be overridden
 # For Kubernetes and ControlPlane, these are the "workload args"
-# Use Thruster HTTP/2 proxy for optimized performance
-CMD ["bundle", "exec", "thrust", "bin/rails", "server"]
+CMD ["./bin/rails", "server"]