feat(validations): merchant (bar/lavazh) ticket validations end-to-end

In-park merchants discharge customers' parking: a merchant user scans the
ticket on their device (/validate; validation:create + program↔user binding)
and applies their program — comp / first-N-minutes free / amount-off (capped,
typed at scan) / percent. All money stays at the booth: the quote folds live
validations in a canonical order (timeCredit → percent → fixed → comp, net
floors at 0, Σ lines ≡ gross − net), the payment records gross/discount and
CONSUMES the validation ids (an overstay's fresh period never re-applies
them), the receipt prints the gross → lines → net story, and the Z/X-report
carries discountTotalMinor leakage. Every apply/void is a signed, attributed
ledger event (refId = append-only void); program config is /setup/site master
data (Bar/Lavazh checkboxes + right-column panel, tabs when both) whose saves
sign config_change. Migration 0024 + reset-db drift-guard entries; 8 route
integration tests + priceSession fold suite.

See wiki/concepts/validation-discounts.md for the full design record.

Claude-Session: https://claude.ai/code/session_01YYkpEsLmoQPaize5ec3oUm

packages/devices/src/interfaces.ts

@@ -275,6 +275,11 @@ export interface ReceiptData {
   readonly voucher: boolean;
   /** Minutes the customer has to reach the exit after paying (voucher mode only). */
   readonly graceExitMin?: number | null;
+  /** Merchant validations (bar/lavazh): the PRE-discount fee and the per-validation
+   *  lines. When present, `amountMinor` is the NET actually paid and the receipt
+   *  shows the full gross → discounts → net story. See validation-discounts.md. */
+  readonly grossMinor?: number | null;
+  readonly validationLines?: readonly { label: string; discountMinor: number }[];
   readonly header?: TicketHeader;
 }