feat(ui): elegant wedding white/silver/gold redesign

Reskin the whole app via design tokens in tailwind-theme.css (remapped
color ramps) plus a define-once component layer in lib/styles/components.css
(.btn, .card, .input, .chip, .badge, .sheet, …). Buttons are muted/outlined
gold rather than flat fills. Self-host Inter + Fraunces (woff2) under the
existing font-src 'self' CSP. Restyle the shared components and the account,
admin, host, join, recover and upload screens against the new tokens.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/lib/components/OnboardingGuide.svelte

@@ -130,8 +130,17 @@
 
 			<!-- Content -->
 			<div class="mb-6 text-center">
-				<div class="mb-3 text-5xl">{currentStep.icon}</div>
-				<h2 id="onboarding-title" class="mb-2 text-xl font-bold text-gray-900 dark:text-gray-100">
+				<div class="mb-4 flex justify-center">
+					<div
+						class="flex h-16 w-16 items-center justify-center rounded-2xl bg-primary-50 text-3xl dark:bg-primary-900/30"
+					>
+						{currentStep.icon}
+					</div>
+				</div>
+				<h2
+					id="onboarding-title"
+					class="mb-2 text-xl font-semibold text-gray-900 dark:text-gray-100"
+				>
 					{currentStep.title}
 				</h2>
 
@@ -193,10 +202,7 @@
 				>
 					Überspringen
 				</button>
-				<button
-					onclick={next}
-					class="flex-1 rounded-xl bg-blue-600 py-3 text-sm font-semibold text-white hover:bg-blue-700 active:bg-blue-700 dark:bg-blue-500 dark:hover:bg-blue-400 dark:active:bg-blue-400"
-				>
+				<button onclick={next} class="btn btn-primary flex-1">
 					{step < steps.length - 1 ? 'Weiter' : "Los geht's!"}
 				</button>
 			</div>