feat(online): use xray online-stats API for onlines and access-log-free IP limit

Adopt xray-core's statsUserOnline policy and GetUsersStats RPC so online
detection is connection-based and IP limiting no longer requires an access
log. Falls back to the legacy traffic-delta onlines and access-log parsing
when the running core lacks the RPCs (Unimplemented), probed lazily per
process so a panel-driven version switch re-evaluates automatically.

Backend:
- xray/api.go: GetOnlineUsers (one GetUsersStats call returns all online
  users and their source IPs) and IsUnimplementedErr.
- xray/process.go: per-process OnlineAPISupport tri-state capability cache.
- service/xray.go: ensureStatsPolicy injects statsUserOnline into every
  policy level of the generated config; XrayService.GetOnlineUsers probes
  and falls back.
- job/xray_traffic_job.go: union API onlines into the delta-derived active
  set; bump last_online for idle-but-connected clients.
- job/check_client_ip_job.go: API-first IP source with shared enforcement;
  live observations bypass the 30-min stale cutoff; access-log path
  unchanged for older cores.
- service/setting.go: GetIpLimitEnable always true; new accessLogEnable
  default for features that genuinely read the access log.

Frontend:
- Client form split into Basic and Config tabs; IP Limit and IP Log no
  longer gated on access log; compact Auto Renew next to Start After First
  Use; tabBasic/tabConfig added to all 13 locales.
- Xray logs button on the dashboard now gated on accessLogEnable.

internal/web/translation/ar-EG.json

@@ -627,6 +627,8 @@
       }
     },
     "clients": {
+      "tabBasic": "أساسي",
+      "tabConfig": "التكوين",
       "add": "إضافة عميل",
       "edit": "تعديل العميل",
       "submitAdd": "إضافة عميل",

internal/web/translation/en-US.json

@@ -628,6 +628,8 @@
       }
     },
     "clients": {
+      "tabBasic": "Basic",
+      "tabConfig": "Config",
       "add": "Add Client",
       "edit": "Edit Client",
       "submitAdd": "Add Client",

internal/web/translation/es-ES.json

@@ -627,6 +627,8 @@
       }
     },
     "clients": {
+      "tabBasic": "Básico",
+      "tabConfig": "Configuración",
       "add": "Añadir cliente",
       "edit": "Editar cliente",
       "submitAdd": "Añadir cliente",

internal/web/translation/fa-IR.json

@@ -627,6 +627,8 @@
       }
     },
     "clients": {
+      "tabBasic": "پایه",
+      "tabConfig": "پیکربندی",
       "add": "افزودن کلاینت",
       "edit": "ویرایش کلاینت",
       "submitAdd": "افزودن کلاینت",

internal/web/translation/id-ID.json

@@ -627,6 +627,8 @@
       }
     },
     "clients": {
+      "tabBasic": "Dasar",
+      "tabConfig": "Konfigurasi",
       "add": "Tambah klien",
       "edit": "Ubah klien",
       "submitAdd": "Tambah klien",

internal/web/translation/ja-JP.json

@@ -627,6 +627,8 @@
       }
     },
     "clients": {
+      "tabBasic": "基本",
+      "tabConfig": "設定",
       "add": "クライアントを追加",
       "edit": "クライアントを編集",
       "submitAdd": "クライアントを追加",

internal/web/translation/pt-BR.json

@@ -627,6 +627,8 @@
       }
     },
     "clients": {
+      "tabBasic": "Básico",
+      "tabConfig": "Configuração",
       "add": "Adicionar cliente",
       "edit": "Editar cliente",
       "submitAdd": "Adicionar cliente",

internal/web/translation/ru-RU.json

@@ -627,6 +627,8 @@
       }
     },
     "clients": {
+      "tabBasic": "Основные",
+      "tabConfig": "Конфигурация",
       "add": "Добавить клиента",
       "edit": "Изменить клиента",
       "submitAdd": "Добавить клиента",

internal/web/translation/tr-TR.json

@@ -628,6 +628,8 @@
       }
     },
     "clients": {
+      "tabBasic": "Temel",
+      "tabConfig": "Yapılandırma",
       "add": "Kullanıcı Ekle",
       "edit": "Kullanıcıyı Düzenle",
       "submitAdd": "Kullanıcı Ekle",

internal/web/translation/uk-UA.json

@@ -627,6 +627,8 @@
       }
     },
     "clients": {
+      "tabBasic": "Основні",
+      "tabConfig": "Конфігурація",
       "add": "Додати клієнта",
       "edit": "Редагувати клієнта",
       "submitAdd": "Додати клієнта",

internal/web/translation/vi-VN.json

@@ -627,6 +627,8 @@
       }
     },
     "clients": {
+      "tabBasic": "Cơ bản",
+      "tabConfig": "Cấu hình",
       "add": "Thêm khách hàng",
       "edit": "Chỉnh sửa khách hàng",
       "submitAdd": "Thêm khách hàng",

internal/web/translation/zh-CN.json

@@ -627,6 +627,8 @@
       }
     },
     "clients": {
+      "tabBasic": "基本",
+      "tabConfig": "配置",
       "add": "添加客户端",
       "edit": "编辑客户端",
       "submitAdd": "添加客户端",

internal/web/translation/zh-TW.json

@@ -627,6 +627,8 @@
       }
     },
     "clients": {
+      "tabBasic": "基本",
+      "tabConfig": "配置",
       "add": "新增客戶端",
       "edit": "編輯客戶端",
       "submitAdd": "新增客戶端",