feat(shift): site-wide single-open shift + booth money-path gate

A shift becomes a SITE-WIDE accountability period — at most one open at a
time — so every taking is unambiguously attributed to one operator. Login
stays decoupled from shifts (an operator can log in off-shift to review).

Backend:
- ShiftService.currentOpenShift()/requireOpenShift(); open() refuses when ANY
  shift is open and throws ShiftAlreadyOpenError{heldBy} (self vs. other).
- requireShift preHandler gates /api/pay, /api/exit, /api/voucher,
  /api/barrier/reopen → 409 {code:"no_shift"}; read-only lookups stay open.
- GET /api/shift/current returns site-wide {open:{startedAt,operator},isMine}.
- GET /api/events?since=<iso> for per-shift log scoping (db: re-export gte).

Frontend:
- Header shift button: open / close-mine / disabled-when-another-holds-it.
- Pay/exit modal gate banner (one-click open; "held by X" when another's);
  pay/exit/voucher disabled until this operator's shift is open.
- Active-Sessions barrier re-open gated the same way.
- Live feed scoped to the open shift's window; shared useShift() Query
  invalidated over the WS on shift_open/shift_z_report/cash_movement.
- sq/en strings for the control + gate.

Wiki: shift.md (site-wide single-open + gate; superseded per-operator note),
booth-console.md (header control + gate), log entry.

Verified: site-wide invariant + heldBy + handover + chain integrity on a
fresh migrated DB (11/11); db/server/web build clean.

apps/web/src/lib/i18n/en.ts

@@ -183,6 +183,20 @@ export const en: Catalog = {
     expectedDrawer: "Expected drawer:",
     printedToReceipt: "Printed to booth receipt.",
     recordedNoPrinter: "Recorded (no printer to print to).",
+    // Header shift control + the booth shift gate.
+    headerNoShift: "No shift",
+    headerOpen: "Open shift",
+    headerClose: "Close shift",
+    headerHeldBy: "Shift open — {{operator}}",
+    headerHeldByShort: "Shift: {{operator}}",
+    gateTitle: "Open a shift to process tickets",
+    gateBody:
+      "No shift is open. Open your shift so payments and exits are recorded against it.",
+    gateOtherTitle: "The open shift belongs to another operator",
+    gateOtherBody:
+      "{{operator}} has an open shift. Only one shift may be open at a time — they must close theirs before you can open yours.",
+    openNow: "Open shift now",
+    opening: "Opening…",
   },
   pay: {
     ticket: "Ticket",

apps/web/src/lib/i18n/sq.ts

@@ -28,7 +28,7 @@ export const sq = {
     site: "Vendi",
   },
   status: {
-    live: "DREJTPËRDREJT",
+    live: "LIVE",
     connecting: "DUKE U LIDHUR",
     offline: "JASHTË LINJE",
   },
@@ -43,7 +43,7 @@ export const sq = {
     uncapped: "pa kufi",
     free: "lirë",
     lotFull: "● parkimi plot",
-    liveFeed: "Aktiviteti i drejtpërdrejtë",
+    liveFeed: "Aktiviteti live",
     events: "ngjarje",
     noEventsYet: "Asnjë ngjarje ende — hyrjet dhe daljet do të shfaqen këtu.",
     activeSessions: "Sesionet aktive",
@@ -185,6 +185,20 @@ export const sq = {
     expectedDrawer: "Arka e pritshme:",
     printedToReceipt: "Printuar te printeri i kabinës.",
     recordedNoPrinter: "Regjistruar (pa printer për të printuar).",
+    // Header shift control + the booth shift gate.
+    headerNoShift: "Asnjë turn",
+    headerOpen: "Hap turnin",
+    headerClose: "Mbyll turnin",
+    headerHeldBy: "Turn i hapur nga {{operator}}",
+    headerHeldByShort: "Turni: {{operator}}",
+    gateTitle: "Hap një turn për të proceduar biletat",
+    gateBody:
+      "Asnjë turn nuk është i hapur. Hap turnin tënd që pagesat dhe daljet të regjistrohen te ky turn.",
+    gateOtherTitle: "Turni i hapur i përket një operatori tjetër",
+    gateOtherBody:
+      "{{operator}} ka një turn të hapur. Vetëm një turn mund të jetë i hapur njëkohësisht — ai duhet të mbyllë turnin para se ti të hapësh tëndin.",
+    openNow: "Hap turnin tani",
+    opening: "Duke hapur…",
   },
   pay: {
     ticket: "Bileta",

apps/web/src/lib/query.ts

@@ -25,4 +25,5 @@ export const qk = {
   events: ["events"] as const,
   activeSessions: ["active-sessions"] as const,
   siteConfig: ["site-config"] as const,
+  shift: ["shift"] as const,
 } as const;

apps/web/src/lib/use-live-feed.ts

@@ -64,6 +64,15 @@ export function useLiveFeed(): void {
           void qc.invalidateQueries({ queryKey: qk.events });
           void qc.invalidateQueries({ queryKey: qk.occupancy });
           void qc.invalidateQueries({ queryKey: qk.activeSessions });
+          // A shift open/close (or a drawer movement) changes the header control
+          // state and the per-shift log window — refresh the shift status too.
+          if (
+            msg.event.type === "shift_open" ||
+            msg.event.type === "shift_z_report" ||
+            msg.event.type === "cash_movement"
+          ) {
+            void qc.invalidateQueries({ queryKey: qk.shift });
+          }
         } else if (msg.kind === "printer-status") {
           void qc.invalidateQueries({ queryKey: ["printers"] });
         }

apps/web/src/lib/use-shift.ts

@@ -0,0 +1,42 @@
+import { useQuery } from "@tanstack/react-query";
+import { fetchShift, type ShiftStatus } from "../api.js";
+import { qk } from "./query.js";
+
+// Shared shift status for the whole app — the header control, the booth screen's
+// per-shift log scope, and the pay/exit modal's gate all read this one Query so
+// they never disagree about whether a shift is open and whose it is. A shift is a
+// SITE-WIDE single-open accountability period (at most one open at a time). The WS
+// invalidates qk.shift on shift_open/shift_z_report/cash_movement, so this stays
+// live without polling. See wiki/concepts/shift.md.
+
+export interface ShiftState {
+  /** Raw status from the server (null while loading / on error). */
+  status: ShiftStatus | undefined;
+  /** Is ANY shift open site-wide? */
+  isOpen: boolean;
+  /** Is the open shift the logged-in operator's (so they may close it / operate)? */
+  isMine: boolean;
+  /** A shift is open but belongs to someone else — this operator is blocked. */
+  blockedByOther: boolean;
+  /** ISO start of the open shift, for scoping the per-shift log. */
+  startedAt: string | null;
+  /** Whoever holds the open shift (for "held by X" messaging). */
+  heldBy: string | null;
+  isLoading: boolean;
+}
+
+export function useShift(): ShiftState {
+  const q = useQuery({ queryKey: qk.shift, queryFn: fetchShift });
+  const s = q.data;
+  const isOpen = s?.open != null;
+  const isMine = s?.isMine ?? false;
+  return {
+    status: s,
+    isOpen,
+    isMine,
+    blockedByOther: isOpen && !isMine,
+    startedAt: s?.open?.startedAt ?? null,
+    heldBy: s?.open?.operator ?? null,
+    isLoading: q.isLoading,
+  };
+}