style: apply Inter + Playfair Display fonts matching reference landing page

- Add Playfair Display as serif font via next/font/google
- Hero headings: font-serif font-medium tracking-tight (was font-extrabold uppercase)
- Body text: font-light (was font-medium)
- Section headings: font-serif tracking-tight (was heavy sans-serif)
- Pricing titles: font-serif font-medium (was font-black uppercase)
- CTA button: rounded-[32px] larger pill style
- Overall softer, more editorial feel matching architectural-grid reference

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

frontend/src/app/globals.css

@@ -7,6 +7,7 @@
   --color-background: var(--background);
   --color-foreground: var(--foreground);
   --font-sans: 'Inter', ui-sans-serif, system-ui, sans-serif;
+  --font-serif: 'Playfair Display', Georgia, serif;
   --font-mono: 'JetBrains Mono', monospace;
 
   /* Brand Colors */
@@ -144,8 +145,8 @@
 
   h1, h2, h3, h4, h5, h6 {
     font-family: 'Inter', ui-sans-serif, system-ui, sans-serif;
-    font-weight: 800;
-    letter-spacing: -0.025em;
+    font-weight: 700;
+    letter-spacing: -0.02em;
     line-height: 1.1;
   }
 
@@ -181,7 +182,7 @@
 }
 
 .premium-button {
-  @apply bg-brand-dark text-white px-8 py-3.5 rounded-xl font-black text-sm transition-all hover:scale-[1.02] active:scale-95;
+  @apply bg-brand-dark text-white px-8 py-3.5 rounded-xl font-bold text-sm transition-all hover:scale-[1.02] active:scale-95;
   box-shadow: 0 4px 14px rgba(26, 26, 26, 0.2);
 }
 .premium-button:hover {
@@ -193,7 +194,7 @@
 }
 
 .accent-pill {
-  @apply px-4 py-1.5 rounded-full border border-brand-accent/30 text-brand-accent text-[11px] font-black uppercase tracking-widest bg-brand-accent/5;
+  @apply px-4 py-1.5 rounded-full border border-brand-accent/30 text-brand-accent text-[11px] font-bold uppercase tracking-widest bg-brand-accent/5;
 }
 .dark .accent-pill {
   @apply border-brand-accent/20;