feat(db): implement read-write splitting for postgres

Add support for database read replicas using the GORM dbresolver plugin. This allows for scaling read operations by distributing them across one or multiple replica nodes.

- Update `DatabaseConfig` to support single and multiple replica configurations.
- Add configuration options for replica connection pooling and selection policy.
- Integrate `dbresolver` in the database initialization process for PostgreSQL.
- Add helper methods to aggregate replica configurations.

internal/model/init.go

@@ -11,6 +11,7 @@ import (
 	"gorm.io/driver/sqlite"
 	"gorm.io/gorm"
 	"gorm.io/gorm/logger"
+	"gorm.io/plugin/dbresolver"
 
 	"with_you/internal/config"
 )
@@ -63,6 +64,40 @@ func NewDB(cfg *config.DatabaseConfig) (*gorm.DB, error) {
 		sqlDB.SetMaxOpenConns(cfg.MaxOpenConns)
 	}
 
+	// 配置读写分离（仅 PostgreSQL 且配置了读副本时生效）
+	if (cfg.Type == "postgres" || cfg.Type == "postgresql") && cfg.HasReplica() {
+		allReplicas := cfg.AllReplicas()
+		replicaDialectors := make([]gorm.Dialector, len(allReplicas))
+		for i, replica := range allReplicas {
+			replicaDialectors[i] = postgres.Open(replica.DSN())
+		}
+
+		replicaMaxIdle := cfg.ReplicaMaxIdle
+		if replicaMaxIdle == 0 {
+			replicaMaxIdle = cfg.MaxIdleConns
+		}
+		replicaMaxOpen := cfg.ReplicaMaxOpen
+		if replicaMaxOpen == 0 {
+			replicaMaxOpen = cfg.MaxOpenConns
+		}
+
+		resolver := dbresolver.Register(dbresolver.Config{
+			Replicas: replicaDialectors,
+		}).
+			SetMaxIdleConns(replicaMaxIdle).
+			SetMaxOpenConns(replicaMaxOpen).
+			SetConnMaxLifetime(time.Hour)
+
+		if err := db.Use(resolver); err != nil {
+			return nil, fmt.Errorf("failed to register dbresolver plugin: %w", err)
+		}
+
+		zap.L().Info("Database read/write splitting configured",
+			zap.String("type", cfg.Type),
+			zap.Int("replica_count", len(allReplicas)),
+		)
+	}
+
 	// 自动迁移
 	if err := autoMigrate(db); err != nil {
 		return nil, fmt.Errorf("failed to auto migrate: %w", err)