fix: add URL validation for GitHub source api_url and html_url fields

Add SafeExternalUrl validation rule that ensures URLs point to
publicly-routable hosts. Apply to all GitHub source entry points
(Livewire Create, Livewire Change, API create and update).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/Unit/SafeExternalUrlTest.php

@@ -0,0 +1,75 @@
+<?php
+
+use App\Rules\SafeExternalUrl;
+use Illuminate\Support\Facades\Validator;
+use Tests\TestCase;
+
+uses(TestCase::class);
+
+it('accepts valid public URLs', function () {
+    $rule = new SafeExternalUrl;
+
+    $validUrls = [
+        'https://api.github.com',
+        'https://github.example.com/api/v3',
+        'https://example.com',
+        'http://example.com',
+    ];
+
+    foreach ($validUrls as $url) {
+        $validator = Validator::make(['url' => $url], ['url' => $rule]);
+        expect($validator->passes())->toBeTrue("Expected valid: {$url}");
+    }
+});
+
+it('rejects private IPv4 addresses', function (string $url) {
+    $rule = new SafeExternalUrl;
+
+    $validator = Validator::make(['url' => $url], ['url' => $rule]);
+    expect($validator->fails())->toBeTrue("Expected rejection: {$url}");
+})->with([
+    'loopback' => 'http://127.0.0.1',
+    'loopback with port' => 'http://127.0.0.1:6379',
+    '10.x range' => 'http://10.0.0.1',
+    '172.16.x range' => 'http://172.16.0.1',
+    '192.168.x range' => 'http://192.168.1.1',
+]);
+
+it('rejects cloud metadata IP', function () {
+    $rule = new SafeExternalUrl;
+
+    $validator = Validator::make(['url' => 'http://169.254.169.254'], ['url' => $rule]);
+    expect($validator->fails())->toBeTrue('Expected rejection: cloud metadata IP');
+});
+
+it('rejects localhost and internal hostnames', function (string $url) {
+    $rule = new SafeExternalUrl;
+
+    $validator = Validator::make(['url' => $url], ['url' => $rule]);
+    expect($validator->fails())->toBeTrue("Expected rejection: {$url}");
+})->with([
+    'localhost' => 'http://localhost',
+    'localhost with port' => 'http://localhost:8080',
+    'zero address' => 'http://0.0.0.0',
+    '.local domain' => 'http://myservice.local',
+    '.internal domain' => 'http://myservice.internal',
+]);
+
+it('rejects non-URL strings', function (string $value) {
+    $rule = new SafeExternalUrl;
+
+    $validator = Validator::make(['url' => $value], ['url' => $rule]);
+    expect($validator->fails())->toBeTrue("Expected rejection: {$value}");
+})->with([
+    'plain string' => 'not-a-url',
+    'ftp scheme' => 'ftp://example.com',
+    'javascript scheme' => 'javascript:alert(1)',
+    'no scheme' => 'example.com',
+]);
+
+it('rejects URLs with IPv6 loopback', function () {
+    $rule = new SafeExternalUrl;
+
+    $validator = Validator::make(['url' => 'http://[::1]'], ['url' => $rule]);
+    expect($validator->fails())->toBeTrue('Expected rejection: IPv6 loopback');
+});