R1: Loadbalancer deploy propagates full proxy deploy_options #1

The loadbalancer tier rebuilds deploy flags from scratch and silently drops the rich per-app options (timeouts, buffering, health checks, path prefixes, error pages), and hardcodes target port :80 ignoring app_port and proxy.run.publish/options.

Fix: Kamal::Commands::Loadbalancer#deploy/#run should reuse Proxy#deploy_options instead of re-implementing flag construction; respect app_port; respect proxy.run.publish/options.

Anchor: lib/kamal/commands/loadbalancer.rb:19-20,37-48. Found via integration failures on 2026-07-03.

Verify: integration suite deploys a multi-host app through the LB with custom proxy settings and they take effect; bin/test.