fix(settings): keep manually set instance public IPs on restart

Closes #11802

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/Feature/GetPublicIpsTest.php

@@ -0,0 +1,60 @@
+<?php
+
+use App\Models\InstanceSettings;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Facades\Process;
+
+uses(RefreshDatabase::class);
+
+beforeEach(function () {
+    Process::fake([
+        'curl -4s https://ifconfig.io' => "203.0.113.1\n",
+        'curl -6s https://ifconfig.io' => "2001:db8::1\n",
+    ]);
+});
+
+it('detects the public IPs when the settings are empty', function () {
+    InstanceSettings::forceCreate(['id' => 0]);
+
+    get_public_ips();
+
+    $settings = InstanceSettings::find(0);
+    expect($settings->public_ipv4)->toBe('203.0.113.1')
+        ->and($settings->public_ipv6)->toBe('2001:db8::1');
+});
+
+it('keeps public IPs that are already set', function () {
+    InstanceSettings::forceCreate(['id' => 0, 'public_ipv4' => '203.0.113.21', 'public_ipv6' => '2001:db8::21']);
+
+    get_public_ips();
+
+    $settings = InstanceSettings::find(0);
+    expect($settings->public_ipv4)->toBe('203.0.113.21')
+        ->and($settings->public_ipv6)->toBe('2001:db8::21');
+    Process::assertNothingRan();
+});
+
+it('detects only the address family that is empty', function () {
+    InstanceSettings::forceCreate(['id' => 0, 'public_ipv4' => '203.0.113.21']);
+
+    get_public_ips();
+
+    $settings = InstanceSettings::find(0);
+    expect($settings->public_ipv4)->toBe('203.0.113.21')
+        ->and($settings->public_ipv6)->toBe('2001:db8::1');
+    Process::assertNotRan('curl -4s https://ifconfig.io');
+});
+
+it('still detects IPv6 when the IPv4 lookup returns an invalid address', function () {
+    Process::fake([
+        'curl -4s https://ifconfig.io' => 'not-an-ip',
+        'curl -6s https://ifconfig.io' => "2001:db8::1\n",
+    ]);
+    InstanceSettings::forceCreate(['id' => 0]);
+
+    get_public_ips();
+
+    $settings = InstanceSettings::find(0);
+    expect($settings->public_ipv4)->toBeNull()
+        ->and($settings->public_ipv6)->toBe('2001:db8::1');
+});