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.

frontend/src/pages/clients/ClientBulkAddModal.tsx

@@ -21,7 +21,6 @@ const MULTI_CLIENT_PROTOCOLS = new Set([
 interface ClientBulkAddModalProps {
   open: boolean;
   inbounds: InboundOption[];
-  ipLimitEnable?: boolean;
   groups?: string[];
   onOpenChange: (open: boolean) => void;
   onSaved?: () => void;
@@ -52,7 +51,6 @@ function emptyForm(): FormState {
 export default function ClientBulkAddModal({
   open,
   inbounds,
-  ipLimitEnable = false,
   groups = [],
   onOpenChange,
   onSaved,
@@ -316,11 +314,9 @@ export default function ClientBulkAddModal({
             </Form.Item>
           )}
 
-          {ipLimitEnable && (
-            <Form.Item label={t('pages.clients.limitIp')}>
-              <InputNumber value={form.limitIp} min={0} onChange={(v) => update('limitIp', Number(v) || 0)} />
-            </Form.Item>
-          )}
+          <Form.Item label={t('pages.clients.limitIp')}>
+            <InputNumber value={form.limitIp} min={0} onChange={(v) => update('limitIp', Number(v) || 0)} />
+          </Form.Item>
 
           <Form.Item label={t('pages.clients.totalGB')}>
             <InputNumber value={form.totalGB} min={0} step={1} onChange={(v) => update('totalGB', Number(v) || 0)} />