Fix --env-file support for the gateway

[dgageot]

No description provided.

[docker-agent]

Review Summary

Assessment: 🟢 APPROVE

Summary

This PR correctly implements --env-file support for gateway configuration by replacing os.Getenv() calls with env.Get(ctx, ...) from the environment provider chain. The change enables reading environment variables from files specified via --env-file while maintaining the existing precedence order.

Analysis:

• All four env.Get() calls correctly ignore the bool return value (which indicates "found" vs "not found")
• The code properly checks for non-empty values (gateway != "", model != "") to determine whether to use the configuration
• I/O errors from reading env files are already handled upstream in computedEnvProvider() before Get() is called
• This pattern matches standard Go conventions and is consistent with the codebase's environment package

Verdict: No issues found. The implementation is correct and follows established patterns in the codebase.

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