fix: preserve telemetry host during deployment

[Icemap]

Summary

• separate the optional workflow input from the application TELEMETRY_PUBLIC_HOST variable
• prevent an omitted workflow input from overriding the server-side .env with an empty process environment value

Validation

• git diff --check
• verified docker compose config --quiet on the deployment host with an empty optional deployment input

Root cause

Docker Compose gives the process environment precedence over --env-file. The workflow exported an empty TELEMETRY_PUBLIC_HOST whenever public_host was omitted, so Compose rejected the otherwise valid server-side configuration before building or restarting the service.