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/ui/Spinner.tsx

@@ -0,0 +1,13 @@
+// Inline busy indicator for buttons whose action can take a moment (opening a
+// shift signs an event over the whole chain; printing waits on hardware). A label
+// swap alone ("Opening…") proved too subtle on the booth — operators re-clicked or
+// assumed the click was lost, so busy buttons pair the text with this spinner.
+// Inherits the button's text colour via border-current.
+export function Spinner() {
+  return (
+    <span
+      aria-hidden
+      className="inline-block h-3 w-3 animate-spin rounded-full border-2 border-current border-t-transparent align-[-1px]"
+    />
+  );
+}