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/Navbar.tsx

@@ -7,7 +7,7 @@ import { useAuth } from "@/hooks/useAuth";
 import { useSiteSettings } from "@/contexts/SiteSettingsContext";
 import { BottomNav } from "./BottomNav";
 import churchLogo from "@/app/church_logo.jpg";
-import { appName, brandColor } from "@/lib/siteConfig";
+import { appName } from "@/lib/siteConfig";
 import { resolveToApiOrigin } from "@/lib/api";
 
 type NavLink = {
@@ -20,11 +20,7 @@ export const Navbar = () => {
     const { user, loading: authLoading, logout } = useAuth();
     const { settings, loading: settingsLoading } = useSiteSettings();
     const pathname = usePathname();
-    // Admin-configurable — applied ONLY to the org name text below via inline
-    // style. No other element in the navbar (or anywhere else) should read
-    // this; everything else uses the fixed brand-* palette.
-    const displayName  = settings.org_name  || appName;
-    const displayColor = settings.accent_color || brandColor;
+    const displayName = settings.org_name || appName;
     const logoSrc      = settings.logo_url ? resolveToApiOrigin(settings.logo_url) : null;
 
     const isActive = (href: string) => {
@@ -79,7 +75,7 @@ export const Navbar = () => {
                             />
                         )}
                         {!settingsLoading && (
-                            <span className="text-xl font-bold" style={{ color: displayColor }}>{displayName}</span>
+                            <span className="text-xl font-bold text-brand-600">{displayName}</span>
                         )}
                     </Link>