How to Build a POS System for Small Business – Claude Code + VS Code + Google Sheets - F4

Build a complete Wood Trading POS system as a 2-file Google Apps Script SPA (Code.gs + index.html).

DOMAIN: A wood trading business that buys wood from suppliers (each shipment = a "Car"),
stocks wood pieces (each with serial, width, length, calculated CFT), and sells via POS.

ROLES: admin, manager, cashier, warehouse_staff — each sees a different dashboard and menu.

SHEETS (one each, all created by setupDemoData):
- Users (id, name, email, phone, password, role, avatar_drive_id, is_active, created_at, updated_at, otp, otp_expires)
- Categories, Sub_Categories (Cars), Suppliers, Customers
- Wood_Stocks (serial, sub_cat, purchase_id, w/l/cft, buy_rate, sell_rate, qty, status, image_drive_id)
- Purchases, Sales, Sale_Items, Payments (unified — supplier_payment / customer_payment)
- Expenses, Import_Logs, Settings (KV), Activity_Logs

FEATURES:
1. Login with email/pwd. Forgot Password sends 6-digit OTP via MailApp,
   stores in Users sheet with 10-min expiry. Reset flow: email → OTP+new pwd.
2. Dashboard: hero with greeting + 3 inline stats, smart auto-alerts,
   6 quick-action cards, KPI grid with today-vs-yesterday trend pills,
   Daily Sales line chart (gradient), Stock Status vertical bar chart,
   Top Customers bar, Expense breakdown donut, unified activity timeline.
3. POS: searchable wood cards with images, qty-picker modal, cart with
   inline qty+rate edit, customer card (gradient when selected), quick-pay
   buttons (Full / Half / None), method tiles with icons, thermal + A4 print.
4. Wood Inventory: DataTable with image thumbnails, image upload to Drive,
   bulk CSV import, sub-category drilldown, stock aging report.
5. Reports: Profit/Loss, Sales Summary, Stock Aging, Customer Analysis,
   Car/Shipment P&L — all with Chart.js + DataTables export.
6. SWR caching: localStorage-backed, instant repaint, silent revalidation.
7. Role-aware menus, server-side role checks on every function.
8. Custom Swal-replacement modals (no external popup CDN).
9. Branded A4 invoice using business_name/address/phone from Settings sheet.

DESIGN: Navy Blue theme. SearchableDropdown for every select.
Loading popup pattern. DataTables 10/page with CSV/PDF/Print buttons.
Mobile bottom nav. Sidebar collapsible, persisted to localStorage.

OUTPUT: Code.gs + index.html only. Use LockService on all writes.
Add the Rameez Scripts header comment block to both files.
Run setupDemoData() to seed April 2026 demo data including all April dates.