chore: clarify server URL environment variables

[alexanderbsingh]

• Clarify that --server-url supports SERVER_URL and BIFROST_SERVER_URL environment variables
• Also fixes a inconsistency where the environment variables took precedence over an explicitly set flag

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (1)

internal/bifrost/options.go:69

• url.Parse will return a nil error for many invalid values (e.g. "example.com" without a scheme/host, or an explicitly passed empty string like --server-url=). With the new env-var precedence logic, an explicitly-set empty/invalid flag value will no longer be overridden by env vars and can make the CLI fail later with a less clear error. Consider validating that the parsed URL has a scheme and host (and rejecting empty) here to fail fast with a clear message.

		}
	}
	_, err := url.Parse(opts.ServerURL)
	if err != nil {
		return err