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/auth/LoginForm.tsx

@@ -84,7 +84,7 @@ export function LoginForm() {
             <button
                 type="button"
                 onClick={() => setShowPassword((s) => !s)}
-                className="absolute right-2 top-1/2 -translate-y-1/2 text-sm text-blue-600"
+                className="absolute right-2 top-1/2 -translate-y-1/2 text-sm text-brand-600"
                 aria-label={showPassword ? "Hide password" : "Show password"}
             >
               {showPassword ? "Hide" : "Show"}
@@ -93,7 +93,7 @@ export function LoginForm() {
           <div className="mt-1">
             <a
                 href="/forgot-password"
-                className="text-xs text-blue-600 hover:underline"
+                className="text-xs text-brand-600 hover:underline"
             >
               Forgot your password?
             </a>
@@ -101,7 +101,7 @@ export function LoginForm() {
           <div className="mt-1">
             <a
                 href={registerHref}
-                className="text-xs text-blue-600 hover:underline"
+                className="text-xs text-brand-600 hover:underline"
             >
               Don't have an account? Sign up here.
             </a>
@@ -120,7 +120,7 @@ export function LoginForm() {
         <button
             type="submit"
             disabled={loading}
-            className="w-full bg-blue-600 text-white rounded py-2 disabled:opacity-60"
+            className="w-full bg-brand-600 hover:bg-brand-700 text-white rounded py-2 disabled:opacity-60"
         >
           {loading ? "Logging in..." : "Login"}
         </button>
@@ -130,7 +130,7 @@ export function LoginForm() {
           <Link
               href="/legal/terms"
               target="_blank"
-              className="text-blue-600 hover:underline"
+              className="text-brand-600 hover:underline"
           >
             Terms of Use
           </Link>{" "}
@@ -138,7 +138,7 @@ export function LoginForm() {
           <Link
               href="/legal/privacy"
               target="_blank"
-              className="text-blue-600 hover:underline"
+              className="text-brand-600 hover:underline"
           >
             Privacy Policy
           </Link>.