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/ClientFormModal.tsx

@@ -28,6 +28,7 @@ import { normalizeClientIps, type ClientIpInfo } from '@/lib/clients/ip-log';
 import { DateTimePicker, SelectAllClearButtons } from '@/components/form';
 import { TLS_FLOW_CONTROL } from '@/schemas/primitives';
 import type { ClientRecord, InboundOption, ExternalLink, ExternalLinkInput } from '@/hooks/useClients';
+import { useFail2banStatusQuery, getLimitIpNotice } from '@/api/queries/useFail2banStatusQuery';
 import { ClientFormSchema, ClientCreateFormSchema } from '@/schemas/client';
 
 const FLOW_OPTIONS = Object.values(TLS_FLOW_CONTROL);
@@ -182,6 +183,9 @@ export default function ClientFormModal({
   const [ipsLoading, setIpsLoading] = useState(false);
   const [ipsClearing, setIpsClearing] = useState(false);
   const [ipsModalOpen, setIpsModalOpen] = useState(false);
+  const fail2ban = useFail2banStatusQuery();
+  const limitIpDisabled = !fail2ban.usable;
+  const limitIpNotice = getLimitIpNotice(fail2ban, t);
 
   function update<K extends keyof FormState>(key: K, value: FormState[K]) {
     setForm((prev) => ({ ...prev, [key]: value }));
@@ -550,17 +554,22 @@ export default function ClientFormModal({
                       </Col>
                       <Col xs={24} md={6}>
                         <Form.Item label={t('pages.clients.limitIp')} tooltip={t('pages.clients.limitIpDesc')}>
-                          <Space.Compact style={{ display: 'flex' }}>
-                            <InputNumber value={form.limitIp} min={0} style={{ flex: 1 }}
-                              onChange={(v) => update('limitIp', Number(v) || 0)} />
-                            {isEdit && (
-                              <Tooltip title={t('pages.clients.ipLog')}>
-                                <Button icon={<EyeOutlined />} loading={ipsLoading} onClick={openIpsModal}>
-                                  {clientIps.length > 0 ? clientIps.length : ''}
-                                </Button>
-                              </Tooltip>
-                            )}
-                          </Space.Compact>
+                          <Tooltip title={limitIpNotice || undefined}>
+                            <span style={{ display: 'flex', width: '100%' }}>
+                              <Space.Compact style={{ display: 'flex', flex: 1 }}>
+                                <InputNumber value={form.limitIp} min={0} disabled={limitIpDisabled}
+                                  style={{ flex: 1, ...(limitIpDisabled ? { pointerEvents: 'none' } : null) }}
+                                  onChange={(v) => update('limitIp', Number(v) || 0)} />
+                                {isEdit && (
+                                  <Tooltip title={t('pages.clients.ipLog')}>
+                                    <Button icon={<EyeOutlined />} loading={ipsLoading} onClick={openIpsModal}>
+                                      {clientIps.length > 0 ? clientIps.length : ''}
+                                    </Button>
+                                  </Tooltip>
+                                )}
+                              </Space.Compact>
+                            </span>
+                          </Tooltip>
                         </Form.Item>
                       </Col>
                     </Row>