Introduced several new classes in the `EnvelopeGenerator.WebUI.Client` namespace:
- Added `Adjustment` class for financial adjustments with deterministic randomization.
- Added `Customer` class to load customer data from a SQL data source with fallback.
- Added `DataItem` class to represent detailed billing data, including adjustments.
- Added `DataItemList` class implementing `IList` for dynamic `DataItem` generation.
- Added `DeterministicRandom` class for reproducible random value generation.
- Added `Term` struct to define payment terms.
- Added `ReportsFactory` class to manage predefined reports.
Updated `MIGRATION_CONTEXT.md` to document the completion of Phase 5 (Data & PredefinedReports Migration) and outline next steps for resolving DevExpress-related errors in Phase 7.
