fix: print new flag errors to stderr and strip whitespace from base64

- Validation errors for -config-env, -config-env-base64 now print to
  stderr and exit 1 instead of going to log.Fatal (which adds a
  timestamp prefix) or silently returning 0.
- Strip surrounding whitespace from the env var value before base64
  decoding to tolerate line-folding by template engines.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Mickaël Canévet <mickael.canevet@proton.ch>

Author: mcanevet

main.go

@@ -9,6 +9,7 @@ import (
 	"io"
 	"log"
 	"os"
+	"strings"
 
 	"github.com/siderolabs/go-adv/adv/talos"
 	"github.com/siderolabs/go-blockdevice/v2/block"
@@ -110,14 +111,16 @@ func main() {
 	}
 
 	if *configPath == "" && *configEnv == "" {
-		fmt.Println("Usage: talos-meta-tool -device <disk-device> (-config <file> | -config-env <VAR> [-config-env-base64])")
-		return
+		fmt.Fprintln(os.Stderr, "Usage: talos-meta-tool -device <disk-device> (-config <file> | -config-env <VAR> [-config-env-base64])")
+		os.Exit(1)
 	}
 	if *configPath != "" && *configEnv != "" {
-		log.Fatal("-config and -config-env are mutually exclusive")
+		fmt.Fprintln(os.Stderr, "-config and -config-env are mutually exclusive")
+		os.Exit(1)
 	}
 	if *configEnvBase64 && *configEnv == "" {
-		log.Fatal("-config-env-base64 requires -config-env")
+		fmt.Fprintln(os.Stderr, "-config-env-base64 requires -config-env")
+		os.Exit(1)
 	}
 
 	device, err := os.OpenFile(*devicePath, os.O_RDWR, 0)
@@ -138,7 +141,7 @@ func main() {
 			log.Fatalf("environment variable %q is not set", *configEnv)
 		}
 		if *configEnvBase64 {
-			configData, err = base64.StdEncoding.DecodeString(val)
+			configData, err = base64.StdEncoding.DecodeString(strings.TrimSpace(val))
 			if err != nil {
 				log.Fatalf("base64 decoding %q: %v", *configEnv, err)
 			}