feat(iplimit): gate IP limit on fail2ban and reset stale limits

Per-client IP limit only enforces where fail2ban is installed, so the panel now reports enforceability and disables the field otherwise:

- Add GET /panel/api/server/fail2banStatus (enabled/installed/usable/windows), cached 30s.
- ClientFormModal and ClientBulkAddModal disable the IP Limit input when not usable and show a hover tooltip; Windows gets a platform-specific message instead of the bash-menu hint.
- One-time migration ResetIpLimitNoFail2ban zeroes existing client limitIp (inbound settings JSON + clients table) on hosts without fail2ban, where the limit never applied.
- Drop the recurring '[LimitIP] Fail2Ban is not installed' warning.
- Add limitIpFail2banMissing/limitIpFail2banWindows/limitIpDisabled across all 13 locales.

frontend/src/pages/clients/ClientBulkAddModal.tsx

@@ -1,6 +1,6 @@
 import { useEffect, useMemo, useState } from 'react';
 import { useTranslation } from 'react-i18next';
-import { AutoComplete, Button, Form, Input, InputNumber, Modal, Select, Space, Switch, message } from 'antd';
+import { AutoComplete, Button, Form, Input, InputNumber, Modal, Select, Space, Switch, Tooltip, message } from 'antd';
 import { ReloadOutlined } from '@ant-design/icons';
 import dayjs from 'dayjs';
 import type { Dayjs } from 'dayjs';
@@ -10,6 +10,7 @@ import { formatInboundLabel } from '@/lib/inbounds/label';
 import { TLS_FLOW_CONTROL } from '@/schemas/primitives';
 import { DateTimePicker, SelectAllClearButtons } from '@/components/form';
 import { useClients, type InboundOption } from '@/hooks/useClients';
+import { useFail2banStatusQuery, getLimitIpNotice } from '@/api/queries/useFail2banStatusQuery';
 import { ClientBulkAddFormSchema, type ClientBulkAddFormValues } from '@/schemas/client';
 
 const FLOW_OPTIONS = Object.values(TLS_FLOW_CONTROL);
@@ -62,6 +63,9 @@ export default function ClientBulkAddModal({
   const [form, setForm] = useState<FormState>(emptyForm);
   const [delayedStart, setDelayedStart] = useState(false);
   const [saving, setSaving] = useState(false);
+  const fail2ban = useFail2banStatusQuery();
+  const limitIpDisabled = !fail2ban.usable;
+  const limitIpNotice = getLimitIpNotice(fail2ban, t);
 
   useEffect(() => {
     if (!open) return;
@@ -311,7 +315,13 @@ export default function ClientBulkAddModal({
           )}
 
           <Form.Item label={t('pages.clients.limitIp')}>
-            <InputNumber value={form.limitIp} min={0} onChange={(v) => update('limitIp', Number(v) || 0)} />
+            <Tooltip title={limitIpNotice || undefined}>
+              <span style={{ display: 'inline-flex' }}>
+                <InputNumber value={form.limitIp} min={0} disabled={limitIpDisabled}
+                  style={limitIpDisabled ? { pointerEvents: 'none' } : undefined}
+                  onChange={(v) => update('limitIp', Number(v) || 0)} />
+              </span>
+            </Tooltip>
           </Form.Item>
 
           <Form.Item label={t('pages.clients.totalGB')}>