refactor: 移除资源用量的可选 Prometheus 接入与平台监控页

- 资源用量弹窗:删除 applyPrometheus/promQueryValue 与峰值/限流字段
  (LOKI_USAGE_PROMETHEUS_URL 从未内置,代码恒走降级),统一提示
  「未接入 Prometheus:暂无峰值/限流数据」;扩容建议改基于 metrics-server 实时值
- 移除「平台监控」菜单页与 /api/v1/system/metrics-summary;
  原始指标保留在标准 /api/v1/metrics(Prometheus 文本格式)可自行抓取
- 手册/落地页/CHANGELOG 同步(去除备份恢复与监控页宣传,指标端点表述中性化)

backend/pkg/metrics/summary.go

@@ -1,106 +0,0 @@
-package metrics
-
-import (
-	"sort"
-
-	dto "github.com/prometheus/client_model/go"
-)
-
-// PathCount 单个路由模板的累计请求数
-type PathCount struct {
-	Path  string  `json:"path"`
-	Count float64 `json:"count"`
-}
-
-// Summary 面板自监控快照:从 registry 聚合出的精简结构(/api/v1/system/metrics-summary)
-type Summary struct {
-	HTTP struct {
-		Total    float64            `json:"total"`
-		ByStatus map[string]float64 `json:"byStatus"`
-		InFlight float64            `json:"inFlight"`
-		TopPaths []PathCount        `json:"topPaths"`
-	} `json:"http"`
-	DB struct {
-		SizeBytes    float64            `json:"sizeBytes"`
-		Saves        float64            `json:"saves"`
-		SaveFailures float64            `json:"saveFailures"`
-		Records      map[string]float64 `json:"records"`
-	} `json:"db"`
-	Alerts struct {
-		Evaluations map[string]float64 `json:"evaluations"`
-	} `json:"alerts"`
-	Loki struct {
-		Queries map[string]float64 `json:"queries"`
-	} `json:"loki"`
-	Runtime struct {
-		Goroutines float64 `json:"goroutines"`
-		GoVersion  string  `json:"goVersion"`
-		Version    string  `json:"version"`
-	} `json:"runtime"`
-}
-
-// Snapshot 聚合当前指标为面板结构(聚合失败返回零值,监控页降级展示)
-func Snapshot() Summary {
-	s := Summary{}
-	s.HTTP.ByStatus = map[string]float64{}
-	s.DB.Records = map[string]float64{}
-	s.Alerts.Evaluations = map[string]float64{}
-	s.Loki.Queries = map[string]float64{}
-
-	families, err := registry.Gather()
-	if err != nil {
-		return s
-	}
-	byPath := map[string]float64{}
-	for _, mf := range families {
-		for _, m := range mf.GetMetric() {
-			labels := labelMap(m)
-			switch mf.GetName() {
-			case "lokistack_http_requests_total":
-				v := m.GetCounter().GetValue()
-				s.HTTP.Total += v
-				s.HTTP.ByStatus[labels["status"]] += v
-				byPath[labels["path"]] += v
-			case "lokistack_http_in_flight_requests":
-				s.HTTP.InFlight = m.GetGauge().GetValue()
-			case "lokistack_db_size_bytes":
-				s.DB.SizeBytes = m.GetGauge().GetValue()
-			case "lokistack_db_save_total":
-				v := m.GetCounter().GetValue()
-				s.DB.Saves += v
-				if labels["result"] != "success" {
-					s.DB.SaveFailures += v
-				}
-			case "lokistack_db_records":
-				s.DB.Records[labels["collection"]] = m.GetGauge().GetValue()
-			case "lokistack_alert_evaluations_total":
-				s.Alerts.Evaluations[labels["result"]] += m.GetCounter().GetValue()
-			case "lokistack_loki_queries_total":
-				s.Loki.Queries[labels["result"]] += m.GetCounter().GetValue()
-			case "go_goroutines":
-				s.Runtime.Goroutines = m.GetGauge().GetValue()
-			case "lokistack_build_info":
-				s.Runtime.GoVersion = labels["go_version"]
-				s.Runtime.Version = labels["version"]
-			}
-		}
-	}
-	paths := make([]PathCount, 0, len(byPath))
-	for p, c := range byPath {
-		paths = append(paths, PathCount{Path: p, Count: c})
-	}
-	sort.Slice(paths, func(i, j int) bool { return paths[i].Count > paths[j].Count })
-	if len(paths) > 8 {
-		paths = paths[:8]
-	}
-	s.HTTP.TopPaths = paths
-	return s
-}
-
-func labelMap(m *dto.Metric) map[string]string {
-	out := map[string]string{}
-	for _, lp := range m.GetLabel() {
-		out[lp.GetName()] = lp.GetValue()
-	}
-	return out
-}