Add Check-in / Ice / Banquet scan modes

- Ice mode: prepaid ice bags (Ice Total / Ice Redeemed columns) redeemed
  independently of ticket check-ins; grab all bags at once or some now.
- Banquet mode: donor total (online + offline) looked up by the ticket's
  email via the Donors Master List, with a manual email override. New
  DonorService + POST /api/banquet.
- Redeem generalized over a resource (tickets|ice); audit records ice actions.
- App gains a mode selector; webhook maps ice_bags (defaults to
  ICE_BAGS_DEFAULT when only a boolean ice option is present).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

INSTALL.md

@@ -53,5 +53,9 @@ Android users can also "Add to Home Screen" from Chrome instead of using Obtaini
 
 ## Using it
 
-- **Scan:** point the camera at a ticket QR. Pick how many people are entering now (a family can split arrivals across the day on one code), then **Check in**. Green + chime = success and the count is saved; red + buzz = a problem (already fully redeemed, not a valid ticket, or a network/database error — the reason is shown).
-- **Admin** (top-right): if scanning won't work, search by **name, email, or ticket code**, then use the buttons to check people in or undo a mistaken check-in.
+Pick a **mode** with the buttons under the title:
+
+- **Check-in** — scan a ticket QR, pick how many people are entering now (a family can split arrivals across the day on one code), then **Check in**. Green + chime = saved; red + buzz = a problem (already fully redeemed, not a valid ticket, or a network/database error — the reason is shown).
+- **Ice** — scan a ticket, hand out prepaid ice bags (defaults to all remaining; adjust if they only want some).
+- **Banquet** — scan a ticket to see that buyer's total donations, or type an email and tap **Look up**.
+- **Admin** (top-right): if scanning won't work, search by **name, email, or ticket code**, use the buttons to check people in or undo, and view check-in history.