PARAM HOSPITAL — GST TAX INVOICE UPGRADE
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What changed
------------
Receptionist > Collect Payment now supports adding several bill items
(Registration Fee, Consultation Fee, Lab Test, etc.) in one go and prints
them as a single GST-style "TAX INVOICE" (matching the Param Hospital
sample layout): hospital GSTIN/PAN/registration no., invoice no., patient
UHID, OPD/IPD & visit details, an itemised table with SAC code / CGST /
SGST / IGST, amount in words, a payment-info box, terms & conditions, an
authorized-signatory block, a "Scan to Verify Invoice" QR and a "Scan to
Pay" UPI QR.

How to apply
------------
1. Import hmsci.sql (new install only), upgrade_existing_database.sql and
   reception_billing_ward_master.sql as before.
2. Import this new file: tax_invoice_upgrade.sql
   (safe to re-run; it only adds columns/settings that do not already
   exist, and never overwrites values you already configured).
3. Open Admin > Settings and fill in the real GSTIN, PAN, hospital
   registration number, website and UPI ID if the defaults inserted by
   the migration are not correct for your hospital (settings.type =
   gstin / pan / hospital_reg_no / hospital_website / upi_id /
   place_of_supply).

Notes
-----
- The QR codes are generated by calling api.qrserver.com from the
  browser when the invoice is opened/printed — the server this app runs
  on needs outbound internet access for those two images to render.
- GST is calculated as 18% (9% CGST + 9% SGST), backed out of the amount
  you enter per item, i.e. the amount you type is treated as the final
  price the patient pays. You can change the GST% per item on the
  Collect Payment screen if a particular service uses a different rate.
- Every patient gets a permanent UHID the first time a bill is printed
  for them (stored on the patient record).
