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/register/[eventId]/RegisterForm.tsx

@@ -207,7 +207,7 @@ function OptionCard({
           {tier ? (
             <>
               <span>R{price.toFixed(2)}</span>
-              <span className="text-indigo-600">
+              <span className="text-brand-600">
                 Early bird — ends {new Date(tier.deadline).toLocaleDateString(undefined, { year: "numeric", month: "short", day: "2-digit" })}
               </span>
             </>
@@ -417,11 +417,11 @@ export default function RegisterForm({ event }: { event: Event }) {
           <div className="text-base font-semibold mb-1">Your details</div>
           <p className="text-sm text-gray-500 mb-3">
             No account needed for this event.{" "}
-            <a href={`/login?redirect=/register/${eventId}`} className="text-indigo-600 hover:underline">Log in</a> if you already have one.
+            <a href={`/login?redirect=/register/${eventId}`} className="text-brand-600 hover:underline">Log in</a> if you already have one.
           </p>
           <div className="space-y-2">
             <input
-              className="w-full border rounded-lg px-3 py-2 text-sm focus:outline-none focus:ring-2 focus:ring-indigo-400"
+              className="w-full border rounded-lg px-3 py-2 text-sm focus:outline-none focus:ring-2 focus:ring-brand-400"
               placeholder="Full name *"
               value={guestName}
               onChange={e => setGuestName(e.target.value)}
@@ -429,7 +429,7 @@ export default function RegisterForm({ event }: { event: Event }) {
             />
             <input
               type="email"
-              className="w-full border rounded-lg px-3 py-2 text-sm focus:outline-none focus:ring-2 focus:ring-indigo-400"
+              className="w-full border rounded-lg px-3 py-2 text-sm focus:outline-none focus:ring-2 focus:ring-brand-400"
               placeholder="Email address *"
               value={guestEmail}
               onChange={e => setGuestEmail(e.target.value)}
@@ -437,7 +437,7 @@ export default function RegisterForm({ event }: { event: Event }) {
             />
             <input
               type="tel"
-              className="w-full border rounded-lg px-3 py-2 text-sm focus:outline-none focus:ring-2 focus:ring-indigo-400"
+              className="w-full border rounded-lg px-3 py-2 text-sm focus:outline-none focus:ring-2 focus:ring-brand-400"
               placeholder="Phone number (optional)"
               value={guestPhone}
               onChange={e => setGuestPhone(e.target.value)}
@@ -486,7 +486,7 @@ export default function RegisterForm({ event }: { event: Event }) {
           <button
             onClick={submitRegistration}
             disabled={creatingRegistration || (!isLoggedIn && !isGuestEligible)}
-            className="bg-blue-600 text-white px-4 py-2 rounded disabled:opacity-60"
+            className="bg-brand-600 text-white px-4 py-2 rounded hover:bg-brand-700 disabled:opacity-60"
           >
             {creatingRegistration ? "Registering..." : "Register"}
           </button>