feat(xray): default outbound in basic routing (#5815)

* feat(xray): default outbound picker in basic routing

Let panel users choose which outbound handles unmatched traffic by
moving it to the first position in the template outbounds list.

* fix(xray): keep direct/blocked outbounds when changing default

* style(routing): revert incidental whitespace churn

Drop double blank lines and the reformatted function signature so the default-outbound diff stays focused on behavior.

frontend/src/test/routing-default-outbound.test.ts

@@ -0,0 +1,51 @@
+import { describe, expect, it } from 'vitest';
+
+import type { XraySettingsValue } from '@/hooks/useXraySetting';
+import { getDefaultOutboundTag, setDefaultOutboundTag } from '@/pages/xray/basics/helpers';
+
+function tpl(
+  outbounds: Array<{ tag?: string; protocol?: string; settings?: unknown }>,
+  rules: Array<{ type: string; outboundTag?: string; ip?: string[]; protocol?: string[] }> = [],
+): XraySettingsValue {
+  return { outbounds, routing: { rules } } as XraySettingsValue;
+}
+
+describe('routing default outbound', () => {
+  it('reads first outbound tag', () => {
+    expect(getDefaultOutboundTag(tpl([{ tag: 'warp', protocol: 'socks' }, { tag: 'direct', protocol: 'freedom' }]))).toBe('warp');
+    expect(getDefaultOutboundTag(tpl([]))).toBe('direct');
+  });
+
+  it('moves existing outbound to first position', () => {
+    const tt = tpl([
+      { tag: 'direct', protocol: 'freedom' },
+      { tag: 'warp', protocol: 'socks' },
+      { tag: 'blocked', protocol: 'blackhole' },
+    ]);
+    setDefaultOutboundTag(tt, 'warp');
+    expect(tt.outbounds!.map((o) => o?.tag)).toEqual(['warp', 'direct', 'blocked']);
+  });
+
+  it('creates blocked outbound when missing', () => {
+    const tt = tpl([{ tag: 'direct', protocol: 'freedom' }]);
+    setDefaultOutboundTag(tt, 'blocked');
+    expect(tt.outbounds![0]?.tag).toBe('blocked');
+    expect(tt.outbounds![0]?.protocol).toBe('blackhole');
+  });
+
+  it('does not prune direct when only blocked rules reference an outbound', () => {
+    const tt = tpl(
+      [
+        { tag: 'direct', protocol: 'freedom', settings: { domainStrategy: 'AsIs' } },
+        { tag: 'blocked', protocol: 'blackhole' },
+        { tag: 'warp', protocol: 'socks' },
+      ],
+      [
+        { type: 'field', ip: ['geoip:private'], outboundTag: 'blocked' },
+        { type: 'field', protocol: ['bittorrent'], outboundTag: 'blocked' },
+      ],
+    );
+    setDefaultOutboundTag(tt, 'warp');
+    expect(tt.outbounds!.map((o) => o?.tag)).toEqual(['warp', 'direct', 'blocked']);
+  });
+});