feat: add SocialAccount model, migration, and factory

Implement SocialAccount model with enum fields for network and type,
along with migration and factory. Includes NETWORKS and TYPES constants
for dropdown usage in Livewire forms and validation.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/Feature/SocialAccountModelTest.php

@@ -0,0 +1,31 @@
+<?php
+
+use App\Models\SocialAccount;
+
+test('a social account can be created with all required fields and a type', function () {
+    $account = SocialAccount::create([
+        'network' => 'twitter',
+        'username' => 'my_handle',
+        'email' => 'handle@example.com',
+        'password' => 'plain-text-password',
+        'type' => 'post',
+    ]);
+
+    expect($account->fresh())
+        ->network->toBe('twitter')
+        ->username->toBe('my_handle')
+        ->email->toBe('handle@example.com')
+        ->password->toBe('plain-text-password')
+        ->type->toBe('post');
+});
+
+test('a social account can be created with a null type', function () {
+    $account = SocialAccount::create([
+        'network' => 'instagram',
+        'username' => 'my_handle',
+        'email' => 'handle@example.com',
+        'password' => 'plain-text-password',
+    ]);
+
+    expect($account->fresh()->type)->toBeNull();
+});