[management,signal,proxy,relay,misc] Unify service configuration loading

Service entry points currently resolve defaults, files, environment variables, and flags differently, which makes precedence inconsistent and prevents some services from using config files.

Introduce one Viper-backed loader and migrate Combined, Management, Relay, Signal, and Proxy while preserving compatibility aliases and Management template expansion.

relay/cmd/env.go

@@ -1,35 +0,0 @@
-package cmd
-
-import (
-	"os"
-	"strings"
-
-	log "github.com/sirupsen/logrus"
-	"github.com/spf13/cobra"
-	"github.com/spf13/pflag"
-)
-
-// setFlagsFromEnvVars reads and updates flag values from environment variables with prefix NB_
-func setFlagsFromEnvVars(cmd *cobra.Command) {
-	flags := cmd.PersistentFlags()
-	flags.VisitAll(func(f *pflag.Flag) {
-		newEnvVar := flagNameToEnvVar(f.Name, "NB_")
-		value, present := os.LookupEnv(newEnvVar)
-		if !present {
-			return
-		}
-
-		err := flags.Set(f.Name, value)
-		if err != nil {
-			log.Infof("unable to configure flag %s using variable %s, err: %v", f.Name, newEnvVar, err)
-		}
-	})
-}
-
-// flagNameToEnvVar converts flag name to environment var name adding a prefix,
-// replacing dashes and making all uppercase (e.g. setup-keys is converted to NB_SETUP_KEYS according to the input prefix)
-func flagNameToEnvVar(cmdFlag string, prefix string) string {
-	parsed := strings.ReplaceAll(cmdFlag, "-", "_")
-	upper := strings.ToUpper(parsed)
-	return prefix + upper
-}