Enhance Group and Document resources; add leader and helper teacher relationships, update navigation icons, and adjust navigation sorting.

app/Models/Teacher.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsToMany;
+use Illuminate\Database\Eloquent\Relations\HasMany;
+
+class Teacher extends Model
+{
+    /** @use HasFactory<\Database\Factories\TeacherFactory> */
+    use HasFactory;
+
+    public function ledGroups(): HasMany
+    {
+        return $this->hasMany(Group::class, 'leader_teacher_id');
+    }
+
+    public function assistedGroups(): BelongsToMany
+    {
+        return $this->belongsToMany(Group::class, 'group_teacher');
+    }
+}