feat: branded favicon (e.) and og-image with wordmark

Replaces the default Next favicon.ico and the solid-navy og-image
placeholder. All generated from the brand tokens (ink bg, gold-bright
accents, Georgia italic):
- app/icon.svg — vector favicon "e." for modern browsers
- app/favicon.ico — 48/32/16 raster fallback
- app/apple-icon.png — 180x180 apple-touch-icon (auto-linked by Next)
- public/og-image.png — 1200x630 wordmark + tagline for link previews

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/icon.svg

@@ -0,0 +1,5 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="64" height="64" viewBox="0 0 64 64">
+  <!-- favicon: la "e." de creeer — ink bg, acento gold-bright (tokens de tailwind.config.ts) -->
+  <rect width="64" height="64" rx="12" fill="#0A1F44"/>
+  <text x="31" y="47" text-anchor="middle" font-family="Georgia, serif" font-style="italic" font-weight="bold" font-size="46" fill="#D4AF37">e.</text>
+</svg>