feat: Initial commit for Saqel Platform architecture, backend, Docker, and documentation

backend/app/Models/Subject.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace App\Models;
+
+use Database\Factories\SubjectFactory;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\HasMany;
+
+class Subject extends Model
+{
+    /** @use HasFactory<SubjectFactory> */
+    use HasFactory;
+
+    protected $fillable = ['name', 'slug'];
+
+    public function courses(): HasMany
+    {
+        return $this->hasMany(Course::class);
+    }
+
+    public function concepts(): HasMany
+    {
+        return $this->hasMany(Concept::class);
+    }
+}