Drop ZHANLU_MODELS and ZHANLU_DEFAULT_MODEL config

Model list is always fetched live from the gateway model-info endpoint, so the
static fallback list was dead config with stale IDs (GLM-4.7 vs zhanlu/glm-4.7).
Default to zhanlu/auto when the request omits model.

internal/config/config.go

@@ -21,8 +21,6 @@ type Config struct {
 	PublicKeyPEM       string
 	PhonePublicKeyPEM  string
 	SM2PrivateKey      string
-	Models             []string
-	DefaultModel       string
 	OpenAIAPIKey       string
 	LoginPassword      string
 	PluginVersion      string
@@ -45,7 +43,6 @@ func Load() (Config, error) {
 		PublicKeyPEM:       getenv("ZHANLU_PUBLIC_KEY_PEM", defaultPublicKeyPEM),
 		PhonePublicKeyPEM:  getenv("ZHANLU_PHONE_PUBLIC_KEY_PEM", defaultPhonePublicKeyPEM),
 		SM2PrivateKey:      getenv("ZHANLU_APIKEY_AUTH_SM2_PRIVATE_KEY", defaultSM2PrivateKey),
-		DefaultModel:       getenv("ZHANLU_DEFAULT_MODEL", "GLM-4.7"),
 		OpenAIAPIKey:       os.Getenv("OPENAI_COMPAT_API_KEY"),
 		LoginPassword:      os.Getenv("ZHANLU_LOGIN_PASSWORD"),
 		PluginVersion:      getenv("ZHANLU_PLUGIN_VERSION", "1.4.2"),
@@ -53,7 +50,6 @@ func Load() (Config, error) {
 		StreamIdleTimout:   durationEnv("ZHANLU_STREAM_IDLE_TIMEOUT", 300*time.Second),
 		Debug:              strings.EqualFold(os.Getenv("ZHANLU_DEBUG"), "true"),
 	}
-	cfg.Models = splitCSV(getenv("ZHANLU_MODELS", "GLM-4.7,MiniMax-M2.5"))
 	cfg.Credentials = auth.Credentials{
 		AccessKey: os.Getenv("ZHANLU_ACCESS_KEY"),
 		SecretKey: os.Getenv("ZHANLU_SECRET_KEY"),
@@ -76,18 +72,6 @@ func getenv(key, fallback string) string {
 	return fallback
 }
 
-func splitCSV(s string) []string {
-	parts := strings.Split(s, ",")
-	out := make([]string, 0, len(parts))
-	for _, p := range parts {
-		p = strings.TrimSpace(p)
-		if p != "" {
-			out = append(out, p)
-		}
-	}
-	return out
-}
-
 func durationEnv(key string, fallback time.Duration) time.Duration {
 	v := strings.TrimSpace(os.Getenv(key))
 	if v == "" {