feat: 自动备份与保留策略、健康持续化与状态页、指标历史与趋势图，并修隧道判定误报与仪表盘布局（v1.2.11）

- 自动备份：每日一份（按最新备份是否在 24h 内判定，重启不重复）、保留份数可配、列表/下载/恢复/删除，恢复前先校验归档；顺手修 writeArchive 逐个检查 tar/gzip/文件 Close()（审查报告 §二）

- 健康持续化：只存状态变更（up/down/unknown）并推导可用率与不可用区间；公开状态页默认关闭、访问码存 SHA-256、按 IP 限流、只暴露域名与可用率

- 隧道判定修复：RouteHealthCandidate 新增 tunnel_known，frps 管理接口不可用时不再把「判不出来」当成「不通」（此前会误报「隧道连续不通」）；汇总与徽标同样区分「无法判定」

- 指标历史：metrics_samples 纵向点表（本机 CPU/内存/磁盘 + 每规则上下行，30 天保留、查询按桶平均、不做降采样表）；仪表盘趋势卡支持 1h/24h/7d

- 仪表盘布局：运行状态并入顶部统计区（运行时长补进「服务」卡）；性能并入系统资源那一行，整行 4 列

- 测试：backup/metrics/frp/api/app 新增用例；gofmt、go build/vet/test、vue-tsc、vite build 全绿

- agent 无改动，AgentVersion 保持 0.12.2

internal/settings/settings.go

@@ -52,25 +52,35 @@ const (
 	KeyNotifyFrpsFailThreshold     = "notify_frps_fail_threshold"
 	KeyNotifyAgentFailThreshold    = "notify_agent_fail_threshold"
 	KeyNotifyDriftCooldownHours    = "notify_drift_cooldown_hours"
-	KeyTrustedProxy                = "trusted_proxy_json"
-	KeyGlobalIPBlacklist           = "global_ip_blacklist"
-	KeyGlobalIPWhitelist           = "global_ip_whitelist"
-	KeyChinaCIDRUpdateHours        = "china_cidr_update_interval_hours"
-	KeyChinaCIDRSourceV4           = "china_cidr_source_url_v4"
-	KeyChinaCIDRSourceV6           = "china_cidr_source_url_v6"
-	KeyChinaCIDRUpdatedAt          = "china_cidr_updated_at"
-	KeyChinaCIDRCountV4            = "china_cidr_count_v4"
-	KeyChinaCIDRCountV6            = "china_cidr_count_v6"
-	KeyChinaCIDRLastError          = "china_cidr_last_error"
-	KeyFRPEnabled                  = "frp_enabled"
-	KeyFRPServerAddr               = "frp_server_addr"
-	KeyFRPServerPort               = "frp_server_port"
-	KeyFRPAuthToken                = "frp_auth_token"
-	KeyFRPTLSEnabled               = "frp_tls_enabled"
-	KeyFRPCustomDomains            = "frp_custom_domains"
-	KeyFRPLastError                = "frp_last_error"
-	KeyFRPStartedAt                = "frp_started_at"
-	KeyNginxGlobalMode             = "nginx_global_mode"
+	KeyBackupAutoEnabled           = "backup_auto_enabled"
+	KeyBackupKeepCount             = "backup_keep_count"
+	KeyRouteHealthEnabled          = "route_health_enabled"
+	KeyStatusPageEnabled           = "status_page_enabled"
+	KeyMetricsHistoryEnabled       = "metrics_history_enabled"
+	// KeyStatusPageCodeHash 存访问码的 SHA-256；明文只在保存请求里出现一次
+	KeyStatusPageCodeHash = "status_page_code_hash"
+	// KeyStatusPageCode 只是「保存请求」里用的字段名，不会被直接写库
+	KeyStatusPageCode        = "status_page_code"
+	KeyNotifyOnBackupFailure = "notify_on_backup_failure"
+	KeyTrustedProxy          = "trusted_proxy_json"
+	KeyGlobalIPBlacklist     = "global_ip_blacklist"
+	KeyGlobalIPWhitelist     = "global_ip_whitelist"
+	KeyChinaCIDRUpdateHours  = "china_cidr_update_interval_hours"
+	KeyChinaCIDRSourceV4     = "china_cidr_source_url_v4"
+	KeyChinaCIDRSourceV6     = "china_cidr_source_url_v6"
+	KeyChinaCIDRUpdatedAt    = "china_cidr_updated_at"
+	KeyChinaCIDRCountV4      = "china_cidr_count_v4"
+	KeyChinaCIDRCountV6      = "china_cidr_count_v6"
+	KeyChinaCIDRLastError    = "china_cidr_last_error"
+	KeyFRPEnabled            = "frp_enabled"
+	KeyFRPServerAddr         = "frp_server_addr"
+	KeyFRPServerPort         = "frp_server_port"
+	KeyFRPAuthToken          = "frp_auth_token"
+	KeyFRPTLSEnabled         = "frp_tls_enabled"
+	KeyFRPCustomDomains      = "frp_custom_domains"
+	KeyFRPLastError          = "frp_last_error"
+	KeyFRPStartedAt          = "frp_started_at"
+	KeyNginxGlobalMode       = "nginx_global_mode"
 )
 
 var Defaults = map[string]string{