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/registration/success/page.tsx

@@ -4,6 +4,7 @@ import { Navbar } from "@/components/layout/Navbar";
 import { Footer } from "@/components/layout/Footer";
 import { useSearchParams, useRouter } from "next/navigation";
 import { useAuth } from "@/hooks/useAuth";
+import { CheckCircle2 } from "lucide-react";
 
 type FormField = { id: string; type: 'yes_no'|'text'|'date'|'numeric'|'statement'|'paragraph'; label: string; isRequired?: boolean; helpText?: string|null };
 
@@ -116,7 +117,12 @@ function RegistrationSuccessContent() {
       <Navbar />
       <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="text-2xl font-semibold mb-2">Registration successful</div>
+          <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">Registration successful</h1>
+          </div>
           <p className="text-gray-700 mb-4">Thank you! Your registration has been created{registrationId ? ` (#${registrationId.slice(0,8)})` : ""}.</p>
           {form?.isRequired && reg ? (
             <div className="mb-6 p-3 border rounded bg-yellow-50 text-yellow-800">
@@ -255,7 +261,7 @@ function AttendeeForms({ reg, form, formsData, setFormsData, setError, setInfo }
         ))}
       </div>
       <div className="mt-3 flex gap-2">
-        <button className="px-3 py-1.5 text-sm rounded bg-indigo-600 text-white hover:bg-indigo-700 disabled:opacity-50" disabled={!canSubmit} onClick={submit}>Submit attendee forms</button>
+        <button className="px-3 py-1.5 text-sm rounded bg-brand-600 text-white hover:bg-brand-700 disabled:opacity-50" disabled={!canSubmit} onClick={submit}>Submit attendee forms</button>
         <button className="px-3 py-1.5 text-sm rounded bg-gray-100 hover:bg-gray-200" onClick={saveDraft}>Save for later</button>
       </div>
     </div>