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/components/layout/BottomNav.tsx

@@ -4,14 +4,14 @@ import Link from "next/link";
 import { usePathname } from "next/navigation";
 import { useAuth } from "@/hooks/useAuth";
 import { Home, Calendar, Phone, LogIn, UserPlus, LayoutDashboard, LogOut } from "lucide-react";
-import { useSiteSettings } from "@/contexts/SiteSettingsContext";
-import { brandColor } from "@/lib/siteConfig";
+import { BRAND_600 } from "@/lib/theme";
 
 export const BottomNav = () => {
     const { user, loading: authLoading, logout } = useAuth();
     const pathname = usePathname();
-    const { settings } = useSiteSettings();
-    const accentColor = settings.accent_color || brandColor;
+    // Fixed brand color — unlike the navbar's org name, nothing here is
+    // admin-configurable (see globals.css for the rule).
+    const accentColor = BRAND_600;
 
     const handleLogout = () => {
         logout();
@@ -32,7 +32,7 @@ export const BottomNav = () => {
     const items: NavItem[] = [
         { href: "/", label: "Home", icon: Home },
         { href: "/events", label: "Events", icon: Calendar },
-        { href: "/#contact", label: "Contact", icon: Phone },
+        { href: "/contact", label: "Contact", icon: Phone },
         ...(authLoading
             ? []
             : user