✨(laporan-admin-kredit): tambah kolom keterangan & kolektibilitas

- Tambah field `keterangan` (TEXT) & `kolektibilitas` (VARCHAR 10) pada tabel laporan_admin_kredit
- Update model LaporanAdminKredit dengan fillable baru
- Tambah dropdown kolektibilitas (1-5: Lancar, DPK, Kurang Lancar, Diragukan, Macet) di form
- Tambah textarea keterangan dengan old() support untuk validasi
- Validasi: `keterangan` nullable|string, `kolektibilitas` nullable|string|in:1..5
- Update controller: simpan field baru dengan DB transaction & error handling
- Migration baru untuk menambah kolom `keterangan` & `kolektibilitas`
- UI/UX: konsistensi styling, responsive grid layout, placeholder informatif
- Testing: form simpan & validasi berhasil, migration jalan tanpa error

database/migrations/2025_09_22_015358_add_keterangan_kolektibilitas_to_laporan_admin_kredit_table.php

@@ -0,0 +1,29 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('laporan_admin_kredit', function (Blueprint $table) {
+            $table->text('keterangan')->nullable()->comment('Keterangan tambahan untuk laporan admin kredit');
+            $table->string('kolektibilitas', 10)->nullable()->comment('Status kolektibilitas kredit');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('laporan_admin_kredit', function (Blueprint $table) {
+            $table->dropColumn(['keterangan', 'kolektibilitas']);
+        });
+    }
+};