refactor: 解决无法正确加载 .env 的问题

backend/internal/config/config_test.go

@@ -0,0 +1,23 @@
+package config
+
+import (
+	"testing"
+)
+
+func TestLoad(t *testing.T) {
+	cfg, err := Load()
+	if err != nil {
+		t.Fatalf("Load() failed: %v", err)
+	}
+
+	if cfg.Server.Port == "" {
+		t.Error("Expected Server.Port to have default value")
+	}
+
+	if cfg.LLM.Provider == "" && cfg.LLM.APIKey == "" {
+		t.Logf("Config loaded - some optional values may be empty (expected if .env not found)")
+	} else {
+		t.Logf("Config loaded successfully. Provider: %s, Model: %s",
+			cfg.LLM.Provider, cfg.LLM.Model)
+	}
+}