nikhilb2/simple-invoicing-free-gst-billing-software ? reverse-engineered prompt

Build me a free GST billing app for Indian small businesses that works in the browser and can also be self hosted. I want to create GST invoices, quotations, credit notes, and e way bills, then download them as PDF. It should also export GSTR 1 as JSON for the GST portal, track inventory and stock levels, manage ledgers and cash or bank accounts, and record payments with dues and overdue reminders.

Please include multiple companies, staff logins with simple roles, custom invoice numbering, financial year handling, and a clean dashboard with sales, tax, and stock summaries. It should support UPI payment QR codes on invoices, public share links for documents, email sending, and basic analytics. If possible, make it feel friendly for non accountants, with a guided first invoice flow and a modern mobile friendly UI. Look up current docs online if you need to.