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/set-banner/page.tsx

@@ -4,6 +4,7 @@ import React, { useEffect, useState } from "react";
 import { useAuth } from "@/hooks/useAuth";
 import { useRouter } from "next/navigation";
 import { apiFetch } from "@/lib/api";
+import { Megaphone } from "lucide-react";
 
 type BannerType = "info" | "warning" | "success" | "danger";
 
@@ -107,8 +108,13 @@ export default function SetBannerPage() {
   return (
     <div className="min-h-screen bg-gray-50 flex items-start justify-center px-4 py-12">
       <div className="w-full max-w-lg border rounded-xl bg-white shadow-sm p-6">
-        <h1 className="text-xl font-semibold mb-1">Site Banner</h1>
-        <p className="text-sm text-gray-500 mb-6">Set a message that appears at the top of every page for visitors within the scheduled window.</p>
+        <div className="flex items-center gap-3 mb-1">
+          <div className="w-10 h-10 rounded-xl bg-brand-50 flex items-center justify-center shrink-0">
+            <Megaphone className="w-5 h-5 text-brand-600" />
+          </div>
+          <h1 className="text-xl font-semibold text-gray-900">Site Banner</h1>
+        </div>
+        <p className="text-sm text-gray-500 mb-6 mt-2">Set a message that appears at the top of every page for visitors within the scheduled window.</p>
 
         <form onSubmit={submit} className="space-y-4">
           <div>
@@ -147,7 +153,7 @@ export default function SetBannerPage() {
           {status && <p className="text-sm text-emerald-700">{status}</p>}
 
           <div className="flex gap-3 pt-1">
-            <button type="submit" disabled={busy} className="px-4 py-2 rounded bg-indigo-600 text-white text-sm disabled:opacity-60 hover:bg-indigo-700">
+            <button type="submit" disabled={busy} className="px-4 py-2 rounded bg-brand-600 text-white text-sm disabled:opacity-60 hover:bg-brand-700">
               {busy ? "Saving…" : "Save banner"}
             </button>
             <button type="button" onClick={clear} disabled={busy} className="px-4 py-2 rounded bg-gray-100 text-gray-700 text-sm disabled:opacity-60 hover:bg-gray-200">