feat: 实现 Redis 会话存储，支持内存/Redis 双模式自动切换

- 新增 go-redis/v9 依赖
- 新增 config.yaml redis 配置段 + RedisConfig 结构体 + REDIS_PASSWORD 环境变量覆盖
- 新增 common/redis.go Redis 客户端初始化
- 完整实现 session/redis_store.go，实现 Store 接口全部 7 个方法
- Redis TTL 自动过期，无须后台清理 goroutine
- deps_core.go 根据 cfg.Redis.Enabled 自动选择 RedisStore/MemoryStore
- router.go + main.go 透传 redisClient 参数

internal/router/deps_extra.go

@@ -8,11 +8,12 @@ import (
 	"metazone.cc/metalab/internal/repository"
 	"metazone.cc/metalab/internal/service"
 
+	"github.com/redis/go-redis/v9"
 	"gorm.io/gorm"
 )
 
-func buildDeps(db *gorm.DB, cfg *config.Config, siteSettings *config.SiteSettings) *dependencies {
-	userRepo, sessionMgr, authService, _, authCtrl, avatarSvc, authMdw, adminController := buildDepsCore(db, cfg, siteSettings)
+func buildDeps(db *gorm.DB, cfg *config.Config, siteSettings *config.SiteSettings, redisClient *redis.Client) *dependencies {
+	userRepo, sessionMgr, authService, _, authCtrl, avatarSvc, authMdw, adminController := buildDepsCore(db, cfg, siteSettings, redisClient)
 
 	auditRepo := repository.NewAuditRepo(db)
 	notificationRepo := repository.NewNotificationRepo(db)