feat: snapshot class_name di setiap presensi & pelanggaran

Migration: tambah kolom:
- attendances.class_name (varchar 100)
- violations.student_class (varchar 100)
- Backfill data existing dari students.class_name

Controller manual: simpan class_name dari form
Sync E-Jurnal: simpan class_name dari lookup student
ViolationService: ambil class_name dari student saat buat
Model: tambah ke fillable

Ini menjamin data historis tetap akurat meskipun
 siswa naik kelas (X→XI→XII) di tahun ajaran baru.

database/migrations/2026_07_24_183600_add_class_name_to_attendance_and_violations.php

@@ -0,0 +1,44 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+use Illuminate\Support\Facades\DB;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        // Add class_name to attendances
+        Schema::table('attendances', function (Blueprint $table) {
+            $table->string('class_name', 100)->nullable()->after('student_id');
+        });
+
+        // Add student_class to violations (can't use 'class' — reserved word)
+        Schema::table('violations', function (Blueprint $table) {
+            $table->string('student_class', 100)->nullable()->after('student_id');
+        });
+
+        // Backfill existing records with current student class_name
+        DB::statement("UPDATE attendances a
+            JOIN students s ON s.id = a.student_id
+            SET a.class_name = s.class_name
+            WHERE a.class_name IS NULL");
+
+        DB::statement("UPDATE violations v
+            JOIN students s ON s.id = v.student_id
+            SET v.student_class = s.class_name
+            WHERE v.student_class IS NULL");
+    }
+
+    public function down(): void
+    {
+        Schema::table('attendances', function (Blueprint $table) {
+            $table->dropColumn('class_name');
+        });
+
+        Schema::table('violations', function (Blueprint $table) {
+            $table->dropColumn('student_class');
+        });
+    }
+};