Refactored `FinancialInvoice` to include new properties (`Description`, `PublicId`, `IsActive`) and methods for managing items and statuses. Introduced `FinancialInvoiceItem` for invoice itemization. Updated `PaymentTransaction` to reference `FinancialInvoice`.
Enhanced repository and application layers with CRUD operations, advanced search functionality, and integration with contracts. Updated `CompanyContext` with `DbSet<FinancialInvoices>` and `DbSet<FinancialInvoiceItem>`.
Created new database tables for `FinancialInvoices` and `FinancialInvoiceItem`, and updated relationships with `PaymentTransactions`. Added DTOs for invoice creation, editing, and searching. Registered `IFinancialInvoiceRepository` for dependency injection.
