M3 收尾: 限流/配额 + 前端骨架屏 + 单端口托管前端

- ratelimit(内存计数): 密钥级每日请求数/Token 配额、用户级每秒速率
  (OT_RATELIMIT_USER_RPS), 超限返回 429
- 网关 Auth 前置配额/限流检查, finishUsage 累计密钥 token 用量
- 前端 Skeleton 组件 + Dashboard/管理总览加载态
- Go 服务托管 web/dist 静态资源(SPA 回退), 单端口即可访问前后端

Co-Authored-By: Claude <noreply@anthropic.com>

server/internal/app/app.go

@@ -10,6 +10,7 @@ import (
 	"github.com/openteam/server/internal/config"
 	"github.com/openteam/server/internal/pkg/crypto"
 	"github.com/openteam/server/internal/pkg/jwt"
+	"github.com/openteam/server/internal/pkg/ratelimit"
 	"github.com/openteam/server/internal/store"
 	"github.com/openteam/server/internal/usage"
 	"gorm.io/gorm"
@@ -23,6 +24,7 @@ type App struct {
 	JWT       *jwt.Manager
 	Usage     *usage.Recorder
 	Health    *channel.HealthMonitor
+	Limit     *ratelimit.Limiter
 	startedAt time.Time
 	ctx       context.Context
 	cancel    context.CancelFunc
@@ -44,6 +46,7 @@ func New(cfg *config.Config) (*App, error) {
 	}
 	a.ctx, a.cancel = context.WithCancel(context.Background())
 	a.Usage = usage.NewRecorder(db)
+	a.Limit = ratelimit.New()
 
 	if err := a.Seed(); err != nil {
 		return nil, err