feat: add shift management functionality

app/Models/Shift.php

@@ -0,0 +1,48 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+
+class Shift extends Model
+{
+    use HasFactory;
+
+    protected $fillable = [
+        'day_of_week',
+        'date',
+        'start_time',
+        'end_time',
+        'is_active',
+        'user_id',
+        'created_by',
+    ];
+
+    protected $casts = [
+        'date' => 'date',
+        'is_active' => 'boolean',
+        'user_id' => 'integer',
+        'created_by' => 'integer',
+    ];
+
+    public function doctor()
+    {
+        return $this->belongsTo(User::class, 'user_id');
+    }
+
+    public function creator()
+    {
+        return $this->belongsTo(User::class, 'created_by');
+    }
+
+    public function scopeActive($query)
+    {
+        return $query->where('is_active', true);
+    }
+
+    public function scopeOpen($query)
+    {
+        return $query->whereNull('user_id');
+    }
+}

app/Models/User.php

@@ -71,4 +71,9 @@ class User extends Authenticatable
     {
         return $this->hasMany(Pet::class, 'owner_id');
     }
+
+    public function shifts()
+    {
+        return $this->hasMany(Shift::class);
+    }
 }