Implement full Square payment review fixes + frontend polish

Implement every finding from the deep payment review (P0-P2, minors,
nitpicks), then close the post-implementation re-review items, then
align card-form typography and roll out the Square trust badge.

Backend - Square API alignment:
- tip_settings.allow_tipping nested under device_options (was top-level:
  terminal tips were silently lost in prod)
- CreateCardOnFile now accepts customerID and sends card.customer_id;
  saved-card (ccof:) charges forward square_customer_id as CustomerID
- New SquareClient methods GetPayment, CreateCustomer, CancelCheckout
- SCA verification_token accepted + forwarded in all charge paths
- ExpMonth/ExpYear -> *int; URL-path id validation; CancelCheckout
  NOT_FOUND-only no-op (dropped unverified NOOP); exported ErrorCode/
  ErrorDetail helpers; mock rejects raw PANs, RList locks, redacts
  emails, ForceRefundPending hook

Backend - money safety:
- sweepManualPendingSquareRefunds reconciles rows WITH square_refund_id
  instead of stranding them forever
- SweepStalePendingPayments reconciles at Square before failing (tri-state:
  leave pending on transport error, rescue completed, fail definitively)
- GetCheckoutStatus cancellation-recheck; terminal CANCELED resolution;
  SweepStaleTerminalCheckouts covers terminal_checkouts table
- till gift-card clawback on definitive failure incl. retry path +
  INSUFFICIENT_FUNDS/ADDRESS_VERIFICATION_FAILURE/TRANSACTION_LIMIT
- cross-user saved-card collision fixed (UNIQUE(user_id,square_card_id))
- customer provisioning (lazy, save-only); one-off/guest mint no customer
- discount preview/apply unified in discounts.go (global-milestone visible
  in preview, N+1 eliminated, redemption counter preserved on failures)
- webhook event_id dedup; refund loop dedup; stale comment fixes
- test-isolation t.Cleanup on committed sweep tests

Frontend:
- SCA tokenizeWithVerification across all charge flows (amount as
  major-units decimal), 5-min token-expiry re-tokenize, verification_token
  in request bodies
- PaymentModal synchronous double-click + zero/negative-amount guards
- till online-card UI wired to /api/admin/till/sale
- policyPopover generalised; new /privacy-policy route; consent checkbox
  copy + Square privacy link
- Square card iframe styled to app typography (Inter 14px, oklch tokens);
  mock form md:text-sm parity
- 'Secure payment powered by Square' badge on all 8 card-payment flows

Schema/docs: terminal_checkouts + square_customer_id + per-user card
constraint in init-script.sql; README migrations; P14 plan + backlog +
Technical Manual updated.

Includes 39 modified/new test files; full backend suite (25 pkgs),
-race on payments+square, and frontend build are green.

backend/handlers/admin/today_test.go

@@ -848,13 +848,17 @@ func TestAdminToday_ExceptionalHours_ClosedDay(t *testing.T) {
 	}
 
 	// Now seed EXCEPTIONAL hours making today CLOSED.
-	// Need: group → hours → application with week_start = Monday of this week
-	weekday := now.Weekday()
+	// Need: group → hours → application with week_start = Monday of this week.
+	// The Monday must be computed in LONDON time (like the handler's isDayOpen),
+	// not UTC — around the 23:00-00:00 UTC boundary UTC and London are on
+	// different days, and a UTC-derived week_start would not overlap the
+	// handler's London date, silently leaving today "open".
+	weekday := londonNow.Weekday()
 	daysSinceMonday := int(weekday) - 1
 	if daysSinceMonday < 0 {
 		daysSinceMonday = 6
 	}
-	monday := now.AddDate(0, 0, -daysSinceMonday)
+	monday := londonNow.AddDate(0, 0, -daysSinceMonday)
 	mondayStr := monday.Format("2006-01-02")
 
 	var groupID int