feat(sub): auto-detect subscription format by User-Agent (Updated) (#5826)

* feat(settings): add subscription format controls

* feat(sub): auto-detect subscription formats

* fix(xray): validate balancer regexes before save

* Revert "fix(xray): validate balancer regexes before save"

This reverts commit 8a208ce71b.

* doc(endpoints): align indent spaces

* doc(settings): improve error message formatting in validateSubUserAgentRegex

- Use NewErrorf with proper formatting instead of NewError with string concatenation
- Add comment explaining the rationale for returning original pattern value
- This preserves the intentional design where empty input is stored as empty
  in the DB and inherited as the runtime default at read time

---------

Co-authored-by: Tomilla <5007859+Tomilla@users.noreply.github.com>
Co-authored-by: Sanaei <ho3ein.sanaei@gmail.com>

frontend/src/pages/settings/SubscriptionGeneralTab.tsx

@@ -1,6 +1,7 @@
-import { Input, InputNumber, Switch, Tabs } from 'antd';
+import { Alert, Button, Input, InputNumber, Switch, Tabs } from 'antd';
 import { BranchesOutlined, CompassOutlined, IdcardOutlined, InfoCircleOutlined, NodeIndexOutlined, SafetyCertificateOutlined, SettingOutlined } from '@ant-design/icons';
 import { useTranslation } from 'react-i18next';
+import { useNavigate } from 'react-router-dom';
 import type { AllSetting } from '@/models/setting';
 import { SettingListItem } from '@/components/ui';
 import { RemarkTemplateField } from '@/components/form';
@@ -15,6 +16,7 @@ interface SubscriptionGeneralTabProps {
 
 export default function SubscriptionGeneralTab({ allSetting, updateSetting }: SubscriptionGeneralTabProps) {
   const { t } = useTranslation();
+  const navigate = useNavigate();
   const { isMobile } = useMediaQuery();
 
   return (
@@ -33,6 +35,20 @@ export default function SubscriptionGeneralTab({ allSetting, updateSetting }: Su
             <SettingListItem paddings="small" title={t('pages.settings.subClashEnableTitle')}>
               <Switch checked={allSetting.subClashEnable} onChange={(v) => updateSetting({ subClashEnable: v })} />
             </SettingListItem>
+            {(allSetting.subJsonEnable || allSetting.subClashEnable) && (
+              <Alert
+                type="info"
+                showIcon
+                style={{ margin: '12px 20px' }}
+                title={t('pages.settings.subFormatsTipTitle')}
+                description={t('pages.settings.subFormatsTipDesc')}
+                action={(
+                  <Button size="small" onClick={() => navigate('/settings#subscription-formats')}>
+                    {t('pages.settings.subFormatsTipAction')}
+                  </Button>
+                )}
+              />
+            )}
             <SettingListItem paddings="small" title={t('pages.settings.subListen')} description={t('pages.settings.subListenDesc')}>
               <Input value={allSetting.subListen} onChange={(e) => updateSetting({ subListen: e.target.value })} />
             </SettingListItem>