fix: address format and lint issues

- Group const declarations with parentheses per gofumpt rules
- Add errInvalidKeyringBackend static error to satisfy err113
- Wrap dynamic error with static error using fmt.Errorf("%w: ...")

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: salmonumbrella

internal/secrets/store.go

@@ -37,13 +37,16 @@ type Token struct {
 	RefreshToken string    `json:"-"`
 }
 
-const keyringPasswordEnv = "GOG_KEYRING_PASSWORD" //nolint:gosec // env var name, not a credential
-const keyringBackendEnv = "GOG_KEYRING_BACKEND"   //nolint:gosec // env var name, not a credential
+const (
+	keyringPasswordEnv = "GOG_KEYRING_PASSWORD" //nolint:gosec // env var name, not a credential
+	keyringBackendEnv  = "GOG_KEYRING_BACKEND"  //nolint:gosec // env var name, not a credential
+)
 
 var (
-	errMissingEmail        = errors.New("missing email")
-	errMissingRefreshToken = errors.New("missing refresh token")
-	errNoTTY               = errors.New("no TTY available for keyring file backend password prompt")
+	errMissingEmail          = errors.New("missing email")
+	errMissingRefreshToken   = errors.New("missing refresh token")
+	errNoTTY                 = errors.New("no TTY available for keyring file backend password prompt")
+	errInvalidKeyringBackend = errors.New("invalid keyring backend")
 )
 
 func allowedBackendsFromEnv() ([]keyring.BackendType, error) {
@@ -55,7 +58,7 @@ func allowedBackendsFromEnv() ([]keyring.BackendType, error) {
 	case "file":
 		return []keyring.BackendType{keyring.FileBackend}, nil
 	default:
-		return nil, fmt.Errorf("invalid %s (expected auto, keychain, or file)", keyringBackendEnv)
+		return nil, fmt.Errorf("%w: %s (expected auto, keychain, or file)", errInvalidKeyringBackend, keyringBackendEnv)
 	}
 }