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/httpapi/auth.go

@@ -15,7 +15,7 @@ import (
 // Type is one of:
 //   - "user":    a row in the users table, authenticated via Basic + bcrypt.
 //   - "service": the -user/-password flag creds (inter-node cluster traffic
-//                and bootstrap), authenticated via a constant-time compare.
+//     and bootstrap), authenticated via a constant-time compare.
 //   - "key":     an API key, authenticated via Bearer + sha256 lookup.
 //
 // Level is the effective access tier: "read" | "write" | "admin". For users it