Add collected_by to invoices — tracks who actually collected the payment

Auto-generated renewal invoices are created by the system, but
collected_by records the real person who collected the money from
the participant. Set on every payment collection via updatePaidAmount.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Domain/Financial/Models/Invoice.php

@@ -46,6 +46,7 @@ class Invoice extends Model
         'last_printed_at',
         'created_by',
         'approved_by',
+        'collected_by',
     ];
 
     protected function casts(): array
@@ -103,6 +104,11 @@ public function approver(): BelongsTo
         return $this->belongsTo(User::class, 'approved_by');
     }
 
+    public function collector(): BelongsTo
+    {
+        return $this->belongsTo(User::class, 'collected_by');
+    }
+
     public function enrollments(): HasMany
     {
         return $this->hasMany(\App\Domain\Training\Models\Enrollment::class);

app/Domain/Financial/Services/InvoiceService.php

@@ -96,6 +96,7 @@ public function updatePaidAmount(Invoice $invoice, int $amount, User $actor): vo
     {
         $invoice->paid_amount += $amount;
         $invoice->due_amount = $invoice->total_amount - $invoice->paid_amount;
+        $invoice->collected_by = $actor->id;
 
         if ($invoice->due_amount <= 0) {
             $invoice->status = $invoice->due_amount < 0

database/migrations/2026_08_09_000002_add_collected_by_to_invoices.php

+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('invoices', function (Blueprint $table) {
+            $table->foreignId('collected_by')->nullable()->after('approved_by')->constrained('users')->nullOnDelete();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('invoices', function (Blueprint $table) {
+            $table->dropForeign(['collected_by']);
+            $table->dropColumn('collected_by');
+        });
+    }
+};