Replace BTCPay payments with free pre-orders + live ready-status

- server.js: order store with K484-XXXX codes, stand assignment, SSE
  status to customers, passcode-gated staff API, persists to .data/
- staff.html at /staff: order board with Mark ready / Collected / Cancel
- index.html: drop BTCPay API key, invoices, QR, BTC price; orders now
  server-backed with live PREPARING -> READY updates and stand location
- e2e-test.js rewritten for the order loop (14 checks, all passing)
- README added; .gitignore covers server/.data

server/.env.example

@@ -1,15 +1,12 @@
-# Copy to .env and fill in. The server also accepts settings at runtime
-# via the ⚙️ settings modal (POST /api/settings), which writes .env for you.
+# KITCHEN 484 server config — copy to .env and edit.
+# The server reads this file at startup (real env vars win).
+
+# Port the server listens on
 PORT=8787
 
-# Your BTCPay Server (regtest: http://localhost:15808, mainnet: https://btcpay.yourhost.com)
-BTCPAY_URL=
-BTCPAY_STORE=
-BTCPAY_API_KEY=
+# Passcode for the staff board (/staff). Staff features stay disabled
+# until this is set. Generate one:  openssl rand -hex 4
+STAFF_PASSCODE=
 
-*** Set automatically by POST /api/webhook/register, or paste it manually
-# after creating a webhook in BTCPay (Store → Settings → Webhooks).
-WEBHOOK_SECRET=
-
-*** Public URL of THIS backend (what BTCPay can reach), e.g. https://kitchen.example.com
-WEBHOOK_PUBLIC_URL=
+# Optional: where orders.json lives (default: server/.data)
+#DATA_DIR=/var/lib/kitchen484