fix: add mass assignment protection to models

Replace $guarded = [] with explicit $fillable whitelists across all
models. Update controllers to use request->only($allowedFields) when
assigning request data. Switch Livewire components to forceFill() for
explicit mass assignment. Add integration tests for mass assignment
protection.

app/Models/User.php

@@ -4,7 +4,9 @@ namespace App\Models;
 
 use App\Jobs\UpdateStripeCustomerEmailJob;
 use App\Notifications\Channels\SendsEmail;
+use App\Notifications\TransactionalEmails\EmailChangeVerification;
 use App\Notifications\TransactionalEmails\ResetPassword as TransactionalEmailsResetPassword;
+use App\Services\ChangelogService;
 use App\Traits\DeletesUserSessions;
 use DateTimeInterface;
 use Illuminate\Database\Eloquent\Factories\HasFactory;
@@ -41,7 +43,16 @@ class User extends Authenticatable implements SendsEmail
 {
     use DeletesUserSessions, HasApiTokens, HasFactory, Notifiable, TwoFactorAuthenticatable;
 
-    protected $guarded = [];
+    protected $fillable = [
+        'name',
+        'email',
+        'password',
+        'force_password_reset',
+        'marketing_emails',
+        'pending_email',
+        'email_change_code',
+        'email_change_code_expires_at',
+    ];
 
     protected $hidden = [
         'password',
@@ -228,7 +239,7 @@ class User extends Authenticatable implements SendsEmail
 
     public function getUnreadChangelogCount(): int
     {
-        return app(\App\Services\ChangelogService::class)->getUnreadCountForUser($this);
+        return app(ChangelogService::class)->getUnreadCountForUser($this);
     }
 
     public function getRecipients(): array
@@ -239,7 +250,7 @@ class User extends Authenticatable implements SendsEmail
     public function sendVerificationEmail()
     {
         $mail = new MailMessage;
-        $url = Url::temporarySignedRoute(
+        $url = URL::temporarySignedRoute(
             'verify.verify',
             Carbon::now()->addMinutes(Config::get('auth.verification.expire', 60)),
             [
@@ -408,7 +419,7 @@ class User extends Authenticatable implements SendsEmail
         ]);
 
         // Send verification email to new address
-        $this->notify(new \App\Notifications\TransactionalEmails\EmailChangeVerification($this, $code, $newEmail, $expiresAt));
+        $this->notify(new EmailChangeVerification($this, $code, $newEmail, $expiresAt));
     }
 
     public function isEmailChangeCodeValid(string $code): bool