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/cluster/ring_engine.go

@@ -162,16 +162,17 @@ func (e *Engine) loadSnapshot() Load {
 
 // OnToken is the SINGLE-ROUND token handler. Per the authoritative design
 // (plan §令牌环协议): on receiving the token a node simultaneously
-//   (a) ADOPTS the carried cluster picture — incoming state is authoritative
-//       for membership + per-node fields. This is safe because structural
-//       changes (join/remove) are NOT kept in local state waiting to survive
-//       a merge: joins ride a separate pendingJoin channel injected INTO the
-//       token here, and a self-remove writes the node out of state so the
-//       downstream merge naturally drops it.
-//   (b) APPLIES the incremental log delta, then re-attaches own fresh entries.
-//   (c) APPENDS own node info (load/version) — skipped if we self-removed.
-//   (d) INJECTS pending newcomers right after ourselves + forwards to them.
-//   (e) Paces via a parallel rhythm timer (max(ops, timer)).
+//
+//	(a) ADOPTS the carried cluster picture — incoming state is authoritative
+//	    for membership + per-node fields. This is safe because structural
+//	    changes (join/remove) are NOT kept in local state waiting to survive
+//	    a merge: joins ride a separate pendingJoin channel injected INTO the
+//	    token here, and a self-remove writes the node out of state so the
+//	    downstream merge naturally drops it.
+//	(b) APPLIES the incremental log delta, then re-attaches own fresh entries.
+//	(c) APPENDS own node info (load/version) — skipped if we self-removed.
+//	(d) INJECTS pending newcomers right after ourselves + forwards to them.
+//	(e) Paces via a parallel rhythm timer (max(ops, timer)).
 func (e *Engine) OnToken(ctx context.Context, tk *Token) (*Token, error) {
 	// Multi-token guard: only the newest leader-stamped token is kept.
 	if tk.SentAt > 0 && e.lastTokenAt > 0 && tk.SentAt < e.lastTokenAt {