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

apps/web/src/router.tsx

@@ -46,6 +46,7 @@ import { DrawerManager } from "./DrawerManager.js";
 import { CARD_PAYMENTS_ENABLED } from "./lib/features.js";
 import { LogsViewer } from "./LogsViewer.js";
 import { BackupSettings } from "./BackupSettings.js";
+import { ValidateScreen } from "./ValidateScreen.js";
 import { RecycleBin } from "./RecycleBin.js";
 import { Profile } from "./Profile.js";
 // Reports pulls in Recharts (~heavy) — lazy-loaded so it stays OUT of the booth's
@@ -458,8 +459,11 @@ function RootLayout() {
       <header className="flex items-center gap-4 border-b border-term-border bg-term-panel px-4 py-2">
         <span className="text-sm font-bold uppercase tracking-widest text-term-amber">▮ Parking</span>
         <nav className="flex items-center gap-1">
-          <NavLink to="/booth" label={t("nav.booth")} />
-          <NavLink to="/shifts" label={t("nav.shifts")} />
+          {show("session:read") && <NavLink to="/booth" label={t("nav.booth")} />}
+          {show("shift:read") && <NavLink to="/shifts" label={t("nav.shifts")} />}
+          {/* The merchant's (bar/lavazh) scan-and-validate screen. Their typical role
+              grants ONLY validation:create, so this is often their whole nav. */}
+          {show("validation:create") && <NavLink to="/validate" label={t("nav.validate")} />}
           {/* Drawer — record cash movements (operator) / review them (admin). Shown if the
               user can do either. See wiki/concepts/shift.md. */}
           {(show("drawer:create") || show("drawer:review")) && (
@@ -523,7 +527,12 @@ function RootLayout() {
 const indexRoute = createRoute({
   getParentRoute: () => rootRoute,
   path: "/",
-  beforeLoad: () => {
+  beforeLoad: ({ context }) => {
+    // A merchant-only user (validation:create without the booth's session:read)
+    // lands on their scan-and-validate screen; everyone else on the booth.
+    if (can(context.user, "validation:create") && !can(context.user, "session:read")) {
+      throw redirect({ to: "/validate" });
+    }
     throw redirect({ to: "/booth" });
   },
 });
@@ -534,6 +543,20 @@ const boothRoute = createRoute({
   component: BoothScreen,
 });
 
+// The merchant (bar/lavazh) scan-and-validate screen — usually the ONLY page a
+// merchant user's role can reach. The server enforces the program↔user binding on
+// apply; this gate is defence in depth. See wiki/concepts/validation-discounts.md.
+const validateRoute = createRoute({
+  getParentRoute: () => rootRoute,
+  path: "/validate",
+  beforeLoad: ({ context }) => requirePerm("validation:create")(context),
+  component: function ValidateRoute() {
+    const { user } = rootRoute.useRouteContext();
+    if (!user) return null;
+    return <ValidateScreen user={user} />;
+  },
+});
+
 // Back-compat redirects for paths that moved. Most config screens live under /setup;
 // Subscriptions/Plans/Tariff-Lab were promoted OUT of /setup into the standalone
 // /subscriptions section (2026-06-21) — redirect the old /setup/* paths too so existing
@@ -779,6 +802,7 @@ const profileRoute = createRoute({
 const routeTree = rootRoute.addChildren([
   indexRoute,
   boothRoute,
+  validateRoute,
   ...legacyRedirects,
   profileRoute,
   shiftRoute,