add shop kiosk app

Standalone Alpine.js POS-style shop at /shop/ for anonymous walk-up
purchases. Filters Snack sheet by shop=1, redirects to HCB with
id:shop marker so payments are findable.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: karmanyaahm

public/shop/.htaccess

@@ -0,0 +1,3 @@
+# /shop/.htaccess  (scoped to this directory only)
+Options -MultiViews
+DirectoryIndex index.html