feat: 对接 PostgreSQL 存储层

backend/cmd/server/main.go

@@ -22,6 +22,7 @@ import (
 	"github.com/hhs/camtalk/internal/session"
 	"github.com/hhs/camtalk/internal/store"
 	"github.com/hhs/camtalk/internal/ws"
+	migrations "github.com/hhs/camtalk/migrations"
 )
 
 // Version 通过构建时 -ldflags 注入，如：
@@ -50,27 +51,39 @@ func main() {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 
+	var userRepo store.UserRepository
+	var msgRepo store.MessageRepository
+
 	if cfg.Storage.Driver == "postgres" {
 		pool, err := store.NewPostgresPool(ctx, cfg.Storage.DSN)
 		if err != nil {
 			logger.Log.Fatalw("failed to connect to postgres", "error", err)
 		}
 		defer pool.Close()
-		logger.Log.Infow("postgres connected", "driver", cfg.Storage.Driver)
-		// TODO: Phase 2 - 初始化 UserRepository 和 MessageRepository
-		_ = pool
+
+		// 执行数据库迁移
+		if err := store.RunMigrations(ctx, pool, migrations.FS); err != nil {
+			logger.Log.Fatalw("failed to run migrations", "error", err)
+		}
+
+		userRepo = store.NewPgUserRepository(pool)
+		msgRepo = store.NewPgMessageRepository(pool)
+		logger.Log.Infow("postgres storage initialized", "driver", cfg.Storage.Driver)
+	} else {
+		userRepo = store.NewMemUserRepository()
+		logger.Log.Info("using in-memory storage")
 	}
 
-	// 初始化 UserRepository（内存模式用于无 DB 场景）
-	var userRepo store.UserRepository
-	userRepo = store.NewMemUserRepository()
-
-	// 初始化 Session Manager（MVP 默认内存实现）
+	// 初始化 Session Manager
 	var sessionMgr session.Manager
-	// TODO: 当 Redis 配置非空时切换为 RedisManager
+	var sessionOpts []session.Option
+	if msgRepo != nil {
+		sessionOpts = append(sessionOpts, session.WithMessageRepository(msgRepo))
+	}
 	sessionMgr = session.NewMemoryManager(
 		time.Duration(cfg.Session.TTL)*time.Minute,
 		cfg.Session.MaxHistory,
+		sessionOpts...,
 	)
 	defer sessionMgr.(*session.MemoryManager).Stop()
 
@@ -141,7 +154,7 @@ func main() {
 	authHandler.RegisterRoutes(apiGroup)
 
 	// Conversation REST 端点
-	convHandler := api.NewConversationHandler(sessionMgr, tokenMgr)
+	convHandler := api.NewConversationHandler(sessionMgr, tokenMgr, msgRepo)
 	convHandler.RegisterRoutes(apiGroup)
 
 	// WebSocket