refactor: 审查修复 — netload 消除重复 /sys 读 + 全项目 gofmt

- netload_linux.go: SampleNetLoad 聚合循环不再对每接口重复
  readIfaceSpeed (snapshot 已汇总 cur.capMbps), 每次采样省 N 次 /sys 读
- gofmt -w: ring.go/ring_engine.go/auth.go/handlers.go/handlers_logs.go/
  handlers_users.go/store.go 结构体字段对齐与注释缩进
- README.md: markdownlint 自动修复 (MD028/MD040)

审查结论: 令牌环本身即互斥协议 — OnToken(收令牌)与 StartRing(发令牌)
在同一节点上由令牌串行化, 不存在需要加锁的竞争; WatchLeader 的读为
良性读, 无需 mutex

internal/store/store.go

@@ -148,10 +148,10 @@ type Forward struct {
 type User struct {
 	ID           int64  `json:"id"`
 	Username     string `json:"username"`
-	PasswordHash string `json:"-"` // never serialized to clients
-	Role         string `json:"role"`        // "admin" | "viewer"
+	PasswordHash string `json:"-"`    // never serialized to clients
+	Role         string `json:"role"` // "admin" | "viewer"
 	Enabled      bool   `json:"enabled"`
-	System       bool   `json:"system"`       // true = flag-synced, UI read-only
+	System       bool   `json:"system"` // true = flag-synced, UI read-only
 	CreatedAt    int64  `json:"createdAt"`
 	LastLoginAt  int64  `json:"lastLoginAt"`
 }
@@ -162,12 +162,12 @@ type User struct {
 type ApiKey struct {
 	ID         int64  `json:"id"`
 	UserID     int64  `json:"userId"`
-	Prefix     string `json:"prefix"`     // first 8 chars of plaintext, for display
+	Prefix     string `json:"prefix"` // first 8 chars of plaintext, for display
 	Label      string `json:"label"`
-	Scope      string `json:"scope"`      // "read" | "write" | "admin"
+	Scope      string `json:"scope"` // "read" | "write" | "admin"
 	CreatedAt  int64  `json:"createdAt"`
 	LastUsedAt int64  `json:"lastUsedAt"`
-	ExpiresAt  int64  `json:"expiresAt"`  // 0 = never expires
+	ExpiresAt  int64  `json:"expiresAt"` // 0 = never expires
 }
 
 const schema = `