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Wiki: shift.md (site-wide single-open + gate; superseded per-operator note),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/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",