polish: consolidate typography to next/font variables, add atelier utility classes

- Remove Google Fonts @import from 4 components (SiteHeader, LandingPageWrapper,
  TestimonialsAndCTA, FeaturesAndStats) — eliminate render-blocking external
  request and font flash
- Replace all unloaded Cormorant Garamond / Playfair Display / DM Sans /
  Plus Jakarta Sans references with the existing next/font variables
  (Fraunces, Manrope, Fragment_Mono) — visual coherence with the design system
- Update 9 pages (blog, brands, changelog, maintenance, protected-example,
  roadmap, security, waitlist, WaitlistForm) to use the loaded Fraunces
- Fix dead --font-geist / --font-jetbrains-mono references in
  admin-design-system.css (now point to --font-manrope / --font-fragment-mono
  which are actually loaded)
- Add atelier-pill, atelier-numerals, atelier-fineprint, atelier-canvas-soft
  utility classes; .atelier-input:focus-visible refined ring
- Add .ha-field-textarea, .ha-scroll, .ha-skeleton to admin design system
- Extend prefers-reduced-motion guard to atelier-enter/stagger/shimmer
- Apply atelier-fineprint to login/not-found/error pages for consistency
- No structural changes; build passes, 0 type errors

src/app/error.tsx

@@ -50,10 +50,7 @@ export default function ErrorPage({
 
         {error.message && (
           <details className="mt-6 text-left">
-            <summary
-              className="text-[10px] tracking-[0.18em] uppercase text-stone-500 hover:text-stone-700 cursor-pointer transition-colors"
-              style={{ fontFamily: "var(--font-fragment-mono)" }}
-            >
+            <summary className="atelier-fineprint cursor-pointer hover:text-stone-900 transition-colors">
               Error details
             </summary>
             <div className="mt-3 rounded-lg border border-stone-200 bg-white/70 backdrop-blur-sm p-3.5 text-xs font-mono text-stone-700 break-words">