feat: Phase 6.2 - Split ReportGenerator into DataAggregator + HtmlExporter + ExcelExporter

- Create DataAggregator service (data aggregation logic)
- Create HtmlExporter service (HTML/preview rendering)
- Create ExcelExporter service (Excel download)
- Refactor ReportGenerator to delegate to services

Tests: 101 passing (319 assertions)

app/Services/Report/ExcelExporter.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace App\Services\Report;
+
+use App\Models\Project;
+use App\DTO\ReportFilters;
+use Maatwebsite\Excel\Facades\Excel;
+use App\Exports\ProjectReportExport;
+use Symfony\Component\HttpFoundation\BinaryFileResponse;
+
+class ExcelExporter
+{
+    public function export(Project $project, ReportFilters $filters, array $data): BinaryFileResponse
+    {
+        $export = new ProjectReportExport($project, $filters, $data);
+        $filename = 'informe_'.$project->name.'_'.now()->format('Ymd_His').'.xlsx';
+
+        return Excel::download($export, $filename);
+    }
+}