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/test/subscription-general-tab.test.tsx

@@ -0,0 +1,29 @@
+import { fireEvent, screen } from '@testing-library/react';
+import { MemoryRouter, useLocation } from 'react-router-dom';
+import { describe, expect, it, vi } from 'vitest';
+
+import { AllSetting } from '@/models/setting';
+import SubscriptionGeneralTab from '@/pages/settings/SubscriptionGeneralTab';
+import { renderWithProviders } from './test-utils';
+
+function LocationProbe() {
+  const location = useLocation();
+  return <output data-testid="location">{location.pathname}{location.hash}</output>;
+}
+
+describe('SubscriptionGeneralTab', () => {
+  it('uses router navigation to open subscription format settings', () => {
+    const allSetting = new AllSetting({ subClashEnable: true });
+
+    renderWithProviders(
+      <MemoryRouter initialEntries={['/settings#subscription']}>
+        <SubscriptionGeneralTab allSetting={allSetting} updateSetting={vi.fn()} />
+        <LocationProbe />
+      </MemoryRouter>,
+    );
+
+    fireEvent.click(screen.getByRole('button', { name: 'Open Sub Formats' }));
+
+    expect(screen.getByTestId('location').textContent).toBe('/settings#subscription-formats');
+  });
+});