feat: migrate store layer to GORM with PostgreSQL support

- Migrate all store packages from raw database/sql to GORM ORM
- Add PostgreSQL support alongside SQLite
- Move EncryptedString type to crypto package for cleaner architecture
- Add automatic encryption/decryption for sensitive fields (API keys, secrets)
- Fix PostgreSQL AutoMigrate conflicts by skipping existing tables
- Fix duplicate /klines route registration
- Update tests to use GORM database connections
- Add database configuration support in config package

api/backtest.go

@@ -824,7 +824,7 @@ func (s *Server) hydrateBacktestAIConfig(cfg *backtest.BacktestConfig) error {
 		return fmt.Errorf("AI model %s is not enabled yet", model.Name)
 	}
 
-	apiKey := strings.TrimSpace(model.APIKey)
+	apiKey := strings.TrimSpace(string(model.APIKey))
 	if apiKey == "" {
 		return fmt.Errorf("AI model %s is missing API Key, please configure it in the system first", model.Name)
 	}