Add admin-configurable branding (colors, logo, favicon) and generic default fallbacks

Site Settings -> Branding now supports a Primary/Secondary/Accent brand color
system applied site-wide (buttons, nav, hover states, links) and to outgoing
email header/CTA colors, plus a favicon upload alongside the existing logo
upload, a live preview panel (website/email x desktop/mobile), and
logo-based color suggestions. The setup wizard's Branding step got the same
treatment. Fixes two related bugs found along the way: the setup wizard's
logo/favicon upload was missing its auth token, and a static favicon.ico in
Next's special app/ convention path was silently overriding the dynamic one.

Also replaces every "Hope Events"/"Hope Family Church" default (org name,
email subjects, WhatsApp messages, report metadata, API docs) with a neutral
"Cross Code" placeholder, and the optional legal settings (operator name, IO
details, website URL, effective date) with obviously-generic placeholders
instead of defaulting to real personal/organisational details -- since this
platform is deployed for multiple organisations. Adds SETTINGS.md documenting
every setting's default behaviour.

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 { BRAND_600 } from "@/lib/theme";
+import { useBrandColorVar } from "@/lib/theme";
 
 export const BottomNav = () => {
     const { user, loading: authLoading, logout } = useAuth();
     const pathname = usePathname();
-    // Fixed brand color — unlike the navbar's org name, nothing here is
-    // admin-configurable (see globals.css for the rule).
-    const accentColor = BRAND_600;
+    // Raw SVG needs a literal hex value — reads the live admin-configurable
+    // primary color off the CSS custom property (see lib/theme.ts).
+    const accentColor = useBrandColorVar("--brand-600");
 
     const handleLogout = () => {
         logout();