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/mem.go

@@ -0,0 +1,95 @@
+// Package collector 提供服务器各项系统指标的采集能力。
+// 本文件实现内存使用率采集，通过解析 Linux /proc/meminfo 获取。
+//
+// 署名 Logan.Li
+package collector
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+
+	"ezops/agent/model"
+)
+
+// kbToGB 将 KB 转换为 GB 的换算系数
+const kbToGB = 1.0 / (1024.0 * 1024.0)
+
+// MemCollector 内存指标采集器，通过解析 /proc/meminfo 获取
+type MemCollector struct{}
+
+// NewMemCollector 创建内存采集器实例
+func NewMemCollector() *MemCollector {
+	return &MemCollector{}
+}
+
+// Collect 采集当前内存指标
+func (m *MemCollector) Collect() (model.MemoryStat, error) {
+	values, err := parseMemInfo()
+	if err != nil {
+		return model.MemoryStat{}, fmt.Errorf("读取内存信息失败: %w", err)
+	}
+
+	totalKB := values["MemTotal"]
+	buffersKB := values["Buffers"]
+	cachedKB := values["Cached"]
+	availableKB := values["MemAvailable"]
+	freeKB := values["MemFree"]
+
+	// 若内核未提供 MemAvailable（较老版本），则按传统方式估算可用内存
+	if availableKB == 0 {
+		availableKB = freeKB + buffersKB + cachedKB
+	}
+
+	usedKB := uint64(0)
+	if totalKB > availableKB {
+		usedKB = totalKB - availableKB
+	}
+
+	stat := model.MemoryStat{
+		TotalGB:  float64(totalKB) * kbToGB,
+		UsedGB:   float64(usedKB) * kbToGB,
+		CachedGB: float64(buffersKB+cachedKB) * kbToGB,
+	}
+	if totalKB > 0 {
+		stat.UsagePercent = float64(usedKB) / float64(totalKB) * 100.0
+	}
+	return stat, nil
+}
+
+// parseMemInfo 解析 /proc/meminfo，返回 字段名 -> 数值(KB) 的映射
+func parseMemInfo() (map[string]uint64, error) {
+	result := make(map[string]uint64)
+
+	f, err := os.Open("/proc/meminfo")
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := scanner.Text()
+		// 形如: MemTotal:       16384000 kB
+		parts := strings.SplitN(line, ":", 2)
+		if len(parts) != 2 {
+			continue
+		}
+		key := strings.TrimSpace(parts[0])
+		valFields := strings.Fields(parts[1])
+		if len(valFields) == 0 {
+			continue
+		}
+		val, err := strconv.ParseUint(valFields[0], 10, 64)
+		if err != nil {
+			continue
+		}
+		result[key] = val
+	}
+	if err := scanner.Err(); err != nil {
+		return nil, err
+	}
+	return result, nil
+}