fix(xray): read and write log.logLevel in the Xray basics tab

xray-core 26.11.9 (#7329) spells the key log.logLevel and still accepts
loglevel. A template written with the new spelling showed "warning" in the
panel, and changing the level added a second loglevel key beside it, leaving
the core to pick between two values.

The select now reads either spelling and saves a single logLevel key.

frontend/src/pages/xray/basics/BasicsTab.tsx

@@ -414,12 +414,15 @@ export default function BasicsTab({
             paddings="small"
             control={
               <Select
-                value={(log.loglevel as string) || 'warning'}
+                value={((log.logLevel ?? log.loglevel) as string) || 'warning'}
                 style={{ width: '100%' }}
                 options={LOG_LEVELS.map((s) => ({ value: s, label: s }))}
                 onChange={(v) =>
                   mutate((tt) => {
-                    if (tt.log) tt.log.loglevel = v;
+                    if (!tt.log) return;
+                    // The core reads either spelling, so keeping both would let the stale one win.
+                    delete tt.log.loglevel;
+                    tt.log.logLevel = v;
                   })
                 }
               />

frontend/src/test/basics-log-level.test.tsx

@@ -0,0 +1,34 @@
+import { describe, it, expect, vi } from 'vitest';
+import { fireEvent, screen } from '@testing-library/react';
+
+import BasicsTab from '@/pages/xray/basics/BasicsTab';
+import type { XraySettingsValue } from '@/hooks/useXraySetting';
+
+import { renderWithProviders } from './test-utils';
+
+// xray-core 26.11.9 (#7329) spells the key log.logLevel and still reads loglevel.
+describe('BasicsTab log level spelling', () => {
+  it('shows a template written as logLevel and saves one key, not both spellings', () => {
+    const setTemplateSettings = vi.fn();
+    renderWithProviders(
+      <BasicsTab
+        templateSettings={{ log: { logLevel: 'debug' } } as unknown as XraySettingsValue}
+        setTemplateSettings={setTemplateSettings}
+        outboundTestUrl=""
+        onChangeOutboundTestUrl={vi.fn()}
+        onResetDefault={vi.fn()}
+      />,
+    );
+    fireEvent.click(screen.getByRole('tab', { name: /Log/ }));
+    const combobox = screen.getByRole('combobox', { name: 'Log Level' });
+    expect(combobox.closest('.ant-select')?.textContent).toContain('debug');
+
+    fireEvent.mouseDown(combobox);
+    fireEvent.click(screen.getByTitle('error'));
+    const update = setTemplateSettings.mock.calls.at(-1)?.[0] as (
+      prev: XraySettingsValue,
+    ) => XraySettingsValue;
+    const legacy = { log: { loglevel: 'warning' } } as unknown as XraySettingsValue;
+    expect(update(legacy).log).toEqual({ logLevel: 'error' });
+  });
+});