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/netload_linux.go

@@ -196,8 +196,9 @@ func SampleNetLoad() float64 {
 	//
 	// rx+tx counts BOTH directions — a forward proxies in AND out, so a NIC
 	// that's saturated in one direction is saturated for forwarding purposes.
+	// Capacity comes from the CURRENT snapshot's capMbps (already summed in
+	// snapshotNet) — no extra /sys reads per interface here.
 	var deltaBits float64
-	sharedCap := uint64(0)
 	for name, c := range cur.bytes {
 		p, ok := prev.bytes[name]
 		if !ok {
@@ -209,15 +210,11 @@ func SampleNetLoad() float64 {
 			continue
 		}
 		deltaBits += float64(c-p) * 8
-		// approximate this interface's capacity contribution proportional to
-		// its share of the summed speed — read back from /sys would be noisy
-		// per call, so reuse the prior snapshot's capMbps scaling.
-		sharedCap += readIfaceSpeed(name)
 	}
-	if sharedCap == 0 {
+	if cur.capMbps == 0 {
 		return 0
 	}
-	capBitsPerSec := float64(sharedCap) * 1e6
+	capBitsPerSec := float64(cur.capMbps) * 1e6
 	pct := (deltaBits / dt) / capBitsPerSec * 100
 	if pct < 0 {
 		return 0