feat: add monitoring agent (Go) + agent report API + cloud billing UI

- Go agent: CPU/mem/disk/port collectors, HTTP report, static binary
- Cross-compile: linux/amd64 + linux/arm64 (statically linked)
- One-line install script for all Linux distros
- Backend: POST /api/v1/agent/report (no JWT) + GET /agent/latest,history (JWT)
- CloudBilling.tsx: fixed syntax errors, stats/trends/records/alerts
- K8s menu renamed to Kubernetes管理

Signed-off-by: Logan.Li

agent/collector/disk.go

@@ -0,0 +1,133 @@
+// Package collector 提供服务器各项系统指标的采集能力。
+// 本文件实现对所有已挂载的真实文件系统执行 statfs，采集磁盘使用情况。
+// 使用 golang.org/x/sys/unix 的 Statfs，兼容 Linux 与 macOS。
+//
+// 署名 Logan.Li
+package collector
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"runtime"
+	"strings"
+
+	"golang.org/x/sys/unix"
+
+	"ezops/agent/model"
+)
+
+// DiskCollector 磁盘使用率采集器
+type DiskCollector struct{}
+
+// NewDiskCollector 创建磁盘采集器实例
+func NewDiskCollector() *DiskCollector {
+	return &DiskCollector{}
+}
+
+// mount 描述一个挂载点信息
+type mount struct {
+	device     string
+	mountpoint string
+	fstype     string
+}
+
+// realFilesystems 允许采集的"真实"文件系统类型白名单，
+// 用于排除 tmpfs/proc/sysfs 等伪文件系统，避免产生噪音数据。
+var realFilesystems = map[string]bool{
+	"ext2": true, "ext3": true, "ext4": true,
+	"xfs": true, "btrfs": true, "zfs": true,
+	"apfs": true, "hfs": true, "exfat": true,
+	"ntfs": true, "vfat": true, "fat32": true,
+	"f2fs": true, "jfs": true, "reiserfs": true,
+	"ufs": true,
+}
+
+// Collect 采集所有真实文件系统挂载点的磁盘使用情况
+func (d *DiskCollector) Collect() ([]model.DiskStat, error) {
+	mounts, err := d.getMounts()
+	if err != nil {
+		return nil, fmt.Errorf("获取挂载点失败: %w", err)
+	}
+
+	disks := make([]model.DiskStat, 0, len(mounts))
+	seen := make(map[string]bool) // 按挂载点去重
+
+	for _, m := range mounts {
+		if !realFilesystems[m.fstype] {
+			continue
+		}
+		if seen[m.mountpoint] {
+			continue
+		}
+		seen[m.mountpoint] = true
+
+		var fs unix.Statfs_t
+		if err := unix.Statfs(m.mountpoint, &fs); err != nil {
+			// 单个挂载点采集失败不影响其余挂载点
+			continue
+		}
+
+		bsize := uint64(fs.Bsize)
+		total := fs.Blocks * bsize
+		free := fs.Bfree * bsize
+		if total == 0 {
+			continue
+		}
+		used := total - free
+
+		disks = append(disks, model.DiskStat{
+			Mount:        m.mountpoint,
+			Device:       m.device,
+			TotalGB:      bytesToGB(total),
+			UsedGB:       bytesToGB(used),
+			UsagePercent: float64(used) / float64(total) * 100.0,
+		})
+	}
+	return disks, nil
+}
+
+// getMounts 获取挂载点列表。
+//   - Linux: 解析 /proc/mounts
+//   - macOS（开发环境）: 返回根分区
+func (d *DiskCollector) getMounts() ([]mount, error) {
+	if runtime.GOOS != "linux" {
+		// 开发环境（macOS）下提供根分区以便本地调试
+		return []mount{{device: "/dev/disk1", mountpoint: "/", fstype: "apfs"}}, nil
+	}
+
+	f, err := os.Open("/proc/mounts")
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	var mounts []mount
+	scanner := bufio.NewScanner(f)
+	// 挂载点路径可能较长，扩大缓冲区
+	scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024)
+	for scanner.Scan() {
+		// 形如: /dev/sda1 / ext4 rw,relatime 0 0
+		fields := strings.Fields(scanner.Text())
+		if len(fields) < 3 {
+			continue
+		}
+		mounts = append(mounts, mount{
+			device:     fields[0],
+			mountpoint: unescapeMount(fields[1]),
+			fstype:     fields[2],
+		})
+	}
+	return mounts, scanner.Err()
+}
+
+// unescapeMount 还原 /proc/mounts 中被转义的挂载点路径（如 \040 -> 空格）
+func unescapeMount(s string) string {
+	return strings.ReplaceAll(s, "\\040", " ")
+}
+
+// bytesToGB 字节数转 GB
+func bytesToGB(b uint64) float64 {
+	const gb = 1024.0 * 1024.0 * 1024.0
+	return float64(b) / gb
+}