chore(#11): Remove unused WalletController + wallet request classes (#103)

* feat(#100): monthly report PDF export

- Install barryvdh/laravel-dompdf
- ExportController::monthlyPdf generates PDF from monthly recap data
- Route GET /api/v1/export/monthly-pdf (auth required)
- Blade view exports/monthly_recap.blade.php
- Feature test MonthlyPdfExportTest covers auth + PDF output

* chore(#11): remove unused WalletController and wallet request classes

Dead code: balance/topup/withdraw/send endpoints have no routes and
user confirmed unused. Removes WalletController, SendMoneyRequest,
WalletAmountRequest, WithdrawRequest.

Author: dhabyap