feat: implement invoice generation, archival system, and financial reporting

[SharifIbrahimDev]

Description

This pull request introduces comprehensive backend enhancements to support automated invoice generation and financial reporting capabilities for the finance team. It ensures compliance, traceability, and accurate revenue tracking across the platform.

Key Features & Changes

• Automated Invoice Generation: Created a robust InvoicesService tied to the PAYMENT_COMPLETED event loop to dynamically generate and archive HTML invoices for successful transactions.
• Invoice Download API: Implemented a secure GET /invoices/:id/download endpoint utilizing NestJS streamable files for efficient document retrieval.
• Payment Reconciliation: Added daily reconciliation reporting logic that aggregates successful transactions and compares expected outcomes.
• Revenue & Refund Tracking: Built endpoints to calculate true net revenue (gross payments minus processed refunds) and isolate subscription vs. one-off revenue streams.
• Tax Reporting: Introduced aggregation logic to calculate total tax liabilities based on historical issued invoices.

Related Issues

• Closes Implement invoice generation and archival system #556
• Closes Add payment reconciliation and reporting #557

Testing & Verification

• Validated date-parsing and range validation guards on all reporting API endpoints.
• Verified successful event interception and non-blocking file streaming for invoice archival.
• Ensured clean TypeScript compilation and correct TypeORM aggregations using Between and In operators.

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