fix(models): null-guard isExpired, remove FK from guarded, add return types and casts

- Add null check to WorkspaceInvitation::isExpired() to prevent null errors
- Remove foreign key columns from protected $guarded to prevent silent mass-assignment drops in Workspace, Link, and Domain models
- Add explicit return types (HasMany, BelongsTo) to User relationship methods
- Add return type to Click::link() relationship method
- Add protected $casts for LinkVariant (weight, clicks_count, conversions_count)

Fixes code quality and type safety issues in domain models.

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

app/Domains/Analytics/Models/Click.php

@@ -3,6 +3,7 @@
 namespace App\Domains\Analytics\Models;
 
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
 
 class Click extends Model
 {
@@ -23,7 +24,7 @@ class Click extends Model
         return parent::save($options);
     }
 
-    public function link()
+    public function link(): BelongsTo
     {
         return $this->belongsTo(\App\Domains\Link\Models\Link::class);
     }

app/Domains/Domain/Models/Domain.php

@@ -7,7 +7,7 @@ use Illuminate\Database\Eloquent\Relations\BelongsTo;
 
 class Domain extends Model
 {
-    protected $guarded = ['id', 'workspace_id'];
+    protected $guarded = ['id'];
 
     protected $casts = [
         'verified_at' => 'datetime',

app/Domains/Link/Models/Link.php

@@ -11,7 +11,7 @@ class Link extends Model
 {
     use SoftDeletes;
 
-    protected $guarded = ['id', 'workspace_id', 'created_by'];
+    protected $guarded = ['id'];
 
     protected static function booted(): void
     {

app/Domains/Link/Models/LinkVariant.php

@@ -9,6 +9,12 @@ class LinkVariant extends Model
 {
     protected $guarded = ['id'];
 
+    protected $casts = [
+        'weight' => 'integer',
+        'clicks_count' => 'integer',
+        'conversions_count' => 'integer',
+    ];
+
     public function link(): BelongsTo
     {
         return $this->belongsTo(Link::class);

app/Domains/Workspace/Models/Workspace.php

@@ -11,7 +11,7 @@ class Workspace extends Model
 {
     use SoftDeletes;
 
-    protected $guarded = ['id', 'owner_id'];
+    protected $guarded = ['id'];
 
     protected static function booted(): void
     {

app/Domains/Workspace/Models/WorkspaceInvitation.php

@@ -26,7 +26,7 @@ class WorkspaceInvitation extends Model
 
     public function isExpired(): bool
     {
-        return $this->expires_at->isPast();
+        return $this->expires_at !== null && $this->expires_at->isPast();
     }
 
     public function isAccepted(): bool

app/Models/User.php

@@ -5,6 +5,8 @@ namespace App\Models;
 // use Illuminate\Contracts\Auth\MustVerifyEmail;
 use Database\Factories\UserFactory;
 use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Relations\HasMany;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
 use Illuminate\Database\Eloquent\SoftDeletes;
 use Illuminate\Foundation\Auth\User as Authenticatable;
 use Illuminate\Notifications\Notifiable;
@@ -49,17 +51,17 @@ class User extends Authenticatable
         ];
     }
 
-    public function workspaces()
+    public function workspaces(): HasMany
     {
         return $this->hasMany(\App\Domains\Workspace\Models\Workspace::class, 'owner_id');
     }
 
-    public function defaultWorkspace()
+    public function defaultWorkspace(): BelongsTo
     {
         return $this->belongsTo(\App\Domains\Workspace\Models\Workspace::class, 'default_workspace_id');
     }
 
-    public function workspaceMemberships()
+    public function workspaceMemberships(): HasMany
     {
         return $this->hasMany(\App\Domains\Workspace\Models\WorkspaceMember::class);
     }