Pos_Invoicing

Description:
Build reporting and export functionality for GST compliance and accounting. System should generate Sales Register, Purchase Register, HSN Summary, ITC Summary, GST Payable summary, and Exception reports.

All reports must be exportable in CSV format with fixed structure, consistent formatting, and CA-friendly fields. Reports should correctly reflect invoices, returns, tax calculations, and ITC adjustments.

The system should also identify data issues (missing HSN, GSTIN, UQC, etc.) through an exceptions report to ensure smooth GST filing.

Acceptance Criteria:

All reports available in CSV format
Fixed column order and consistent structure
Date format: YYYY-MM-DD
Amount format: 2 decimal precision
Sales and Purchase registers reconcile with totals
Returns reflected as negative values
HSN summary includes UQC and correct aggregation
GST payable correctly calculated (output - input)
ITC values correctly reflected and adjusted
Exception report identifies missing/invalid data
CSV files open correctly in Excel/Sheets without formatting issues