Full site redesign, help system, and dashboard stats fixes

Multi-phase visual facelift (design tokens, dashboards, sidebar/navbar
shell, per-page help guides, and a layout/content pass across every
remaining page) plus backend fixes to the dashboard KPI stats:

- Admin/Supervisor dashboard KPIs (revenue, donations, registrations,
  tickets sold) now use a rolling trailing-month window (today back one
  calendar month, e.g. 9 May - 8 June if today is 8 June) instead of
  calendar month-to-date, which under-counted for most of the month.
  The comparison window shifts the same way, so like is still compared
  with like.
- Reports deep-links from those stat tiles now match the same window
  (range=trailing_month, replacing range=this_month).
- Design tokens (brand-* Tailwind scale + shadcn CSS variables), a
  site-wide contextual help button, fixed dashboard sidebar/navbar,
  Admin/Supervisor/Staff/User dashboard rebuilds backed by a new
  GET /api/stats/overview endpoint, a dedicated Contact page, Site
  Settings restyle with WhatsApp config folded in, and an Account
  activity feed backed by a new SecurityEvent model.
- Every remaining page (home, events, registration flow, auth, legal,
  payment results, and every Admin/Supervisor/Staff/User tool page)
  restyled onto the same design tokens, several with real layout
  upgrades (home hero, events list/detail, donate page, auth pages).
- 20+ new dedicated help guides so the whole site has page-specific
  help content instead of falling back to a generic guide.
- Assorted fixes surfaced along the way: donation-leg double-counting
  in payment stats, donations not counting toward revenue, refund
  netting in per-method report breakdowns, and donation
  over-allocation after a refund.

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

frontend/src/app/payment/success/page.tsx

@@ -4,6 +4,7 @@ import { Navbar } from "@/components/layout/Navbar";
 import { Footer } from "@/components/layout/Footer";
 import { useRouter } from "next/navigation";
 import { useSiteSettings } from "@/contexts/SiteSettingsContext";
+import { CheckCircle2 } from "lucide-react";
 import React from "react";
 
 export default function PaymentSuccessPage() {
@@ -14,25 +15,32 @@ export default function PaymentSuccessPage() {
   return (
     <div className="min-h-screen flex flex-col">
       <Navbar />
-      <main className="flex-1 p-6 max-w-2xl mx-auto w-full">
-        <h1 className="text-2xl font-semibold mb-2">Payment successful</h1>
-        <p className="text-gray-700">
-          Thank you! Your payment was received. Your tickets will be sent to you shortly.
-          {contactEmail && (
-            <>
-              {" "}If you have any questions, contact us at{" "}
-              <a href={`mailto:${contactEmail}`} className="text-blue-600 hover:underline">
-                {contactEmail}
-              </a>.
-            </>
-          )}
-        </p>
-        <button
-          className="mt-4 px-3 py-1.5 text-sm rounded bg-indigo-100 hover:bg-indigo-200 text-indigo-800 shadow-sm"
-          onClick={() => router.push('/dashboard/user')}
-        >
-          Go to Dashboard
-        </button>
+      <main className="flex-1 px-4 py-10 max-w-2xl mx-auto w-full">
+        <div className="border rounded-xl p-6 bg-white shadow-sm">
+          <div className="flex items-center gap-3 mb-2">
+            <div className="w-10 h-10 rounded-xl bg-green-50 flex items-center justify-center shrink-0">
+              <CheckCircle2 className="w-5 h-5 text-green-600" />
+            </div>
+            <h1 className="text-2xl font-semibold text-gray-900">Payment successful</h1>
+          </div>
+          <p className="text-gray-700 mb-4">
+            Thank you! Your payment was received. Your tickets will be sent to you shortly.
+            {contactEmail && (
+              <>
+                {" "}If you have any questions, contact us at{" "}
+                <a href={`mailto:${contactEmail}`} className="text-brand-600 hover:underline">
+                  {contactEmail}
+                </a>.
+              </>
+            )}
+          </p>
+          <button
+            className="px-4 py-2 rounded-lg bg-brand-600 hover:bg-brand-700 text-white text-sm font-medium transition-colors"
+            onClick={() => router.push('/dashboard/user')}
+          >
+            Go to Dashboard
+          </button>
+        </div>
       </main>
       <Footer />
     </div>