Fix financial double-counting, rebuild cashup accountability, and redesign the Reports page

Financial correctness (donation-leg model):
- Donations are no longer mutated when assigned to a registration; assignment now
  creates an immutable "leg" record referencing the original donation instead.
- Fixed several places where money was double-counted once a donation was partially
  or fully assigned (Payments, Revenue summary, Cashup reconciliation, Finance
  report, Profit report, Master Orders, Revenue Detailed).
- Payments now record who recorded them (recordedBy), separate from who they're for.

Cashup:
- Per-user cash denomination counting (optional, any time) replaces the single
  event-wide manual entry; the event's cash actual is the live sum of these counts.
- New "Payment accountability by staff member" breakdown across all methods, and a
  read-only "Report" tab that opens automatically once an event is closed.

Reports page redesign:
- New shell: sidebar of universal filters (events, date range, past/inactive/closed
  toggles), searchable/categorized report grid, and a popup viewer with
  Print/Email/Excel/WhatsApp actions plus an in-app Reporting Guide.
- Visual pass: colored stat tiles and bar charts on most reports, matching mockups.
- PDF exports (download/Print/Email/WhatsApp) now share a branded design mirroring
  the web report — colored header, stat tiles, bar chart, highlighted totals.
- Excel export now produces a styled .xlsx (via exceljs) instead of a plain CSV.
- Master Orders' "Donations made" table is now included in every export channel.

Bug fixes discovered while testing exports:
- Report emails now go through the shared, DB-configurable mail utility instead of
  a one-off transporter that ignored Site Settings SMTP config.
- WhatsApp report sends now surface the actual WAWP API error and auto-recover a
  disconnected session, instead of a bare axios status-code message.

Also: Admin-editable notification preference, richer Admin Registrations dashboard,
{{payment.link}} placeholder for Email/WhatsApp Attendees, and background
email/WhatsApp attendee sending.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/app/dashboard/supervisor/reports/page.tsx

@@ -7,13 +7,8 @@ import ReportsV2 from "@/components/reports/ReportsV2";
 export default function SupervisorReportsPage() {
   const router = useRouter();
   return (
-    <div className="max-w-6xl mx-auto w-full p-6">
-      <div className="flex items-center justify-between mb-4">
-        <h1 className="text-2xl font-semibold">Reports</h1>
-        <button className="px-3 py-1.5 text-sm rounded bg-gray-100 hover:bg-gray-200 text-gray-800 shadow-sm" onClick={() => router.push('/dashboard')}>Back</button>
-      </div>
-      <p className="text-sm text-gray-600 mb-4">View, export, or email operational reports for events.</p>
-      <ReportsV2 />
+    <div className="w-full p-6">
+      <ReportsV2 onBack={() => router.push('/dashboard')} />
     </div>
   );
 }