feat(drawer): drawer hub — balance now, this-shift figure, daily activity, shift history; busy spinners

/drawer was record + review only: no current balance, no sight of the open
shift's incomings, no daily activity, no shift history. Rebuilt as a hub:

- Drawer now: the till's running balance (new GET /api/drawer/balance,
  shift:read — exposes the service's existing drawerBalance(); the drawer
  is one site-wide till, same exposure the X-report already had) with the
  open shift's X-report breakdown alongside (float + takings + vouchers =
  expected = balance) and a "This shift: ±X" figure (expected − opening
  float — the shift's own contribution vs what it inherited).
- Today's cash activity: every cash payment + voucher since local
  midnight from the signed chain, live, with day totals (card never
  enters the till).
- Record + movements/review: the 2026-07-01 flow, unchanged.
- Closed shifts: drawer-focused history via the scope-aware /api/shifts
  (float → takings ± vouchers → expected per shift).

Also: every shift open/close button (header, /shifts, pay modal, end-
shift confirm) now shows an animated spinner + dims while busy — the old
label-swap-only feedback read as a dead click when a shift open ran slow.
The slowness itself (drawer/shift reads fold the WHOLE chain, O(chain))
is recorded as an open item in wiki/concepts/shift.md with the fix
sketch: fold from the last z-report's signed expectedDrawerMinor forward.

No new ledger surface — one read-only endpoint; RBAC test added.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

apps/web/src/BoothPayModal.tsx

@@ -21,6 +21,7 @@ import { useShift } from "./lib/use-shift.js";
 import { formatDuration, formatMoney, formatTime, formatRelativeDateTime } from "./lib/format.js";
 import { CARD_PAYMENTS_ENABLED } from "./lib/features.js";
 import { SnapshotStrip } from "./ui/SnapshotStrip.js";
+import { Spinner } from "./ui/Spinner.js";
 
 // The booth pay/exit modal. Opened when the operator submits a ticket id. Shows the
 // session (entry, exit=now, duration, total owed) + entry/exit snapshots, takes
@@ -281,7 +282,13 @@ export function BoothPayModal({ identity, onClose }: { identity: string; onClose
                       disabled={openingShift}
                       className="btn btn-go btn-sm mt-2"
                     >
-                      {openingShift ? t("shift.opening") : t("shift.openNow")}
+                      {openingShift ? (
+                        <span className="inline-flex items-center gap-1.5">
+                          <Spinner /> {t("shift.opening")}
+                        </span>
+                      ) : (
+                        t("shift.openNow")
+                      )}
                     </button>
                   </>
                 )}