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

backend/app/Models/Course.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace App\Models;
+
+use Database\Factories\CourseFactory;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\HasMany;
+
+class Course extends Model
+{
+    /** @use HasFactory<CourseFactory> */
+    use HasFactory;
+
+    protected $fillable = ['subject_id', 'grade', 'track', 'title', 'description'];
+
+    public function subject(): BelongsTo
+    {
+        return $this->belongsTo(Subject::class);
+    }
+
+    public function lessons(): HasMany
+    {
+        return $this->hasMany(Lesson::class)->orderBy('order_index');
+    }
+}