feat: centralize frontend branding

frontend/public/images/brand/logo-mark.svg

@@ -0,0 +1,11 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 96 96" role="img" aria-labelledby="title">
+  <title id="title">Socialize mark</title>
+  <defs>
+    <linearGradient id="brand-gradient" x1="16" y1="12" x2="82" y2="88" gradientUnits="userSpaceOnUse">
+      <stop offset="0" stop-color="#ff8a3d"/>
+      <stop offset="1" stop-color="#ef4444"/>
+    </linearGradient>
+  </defs>
+  <rect width="96" height="96" rx="28" fill="url(#brand-gradient)"/>
+  <path d="M31 61.5c3.9 4.3 9.3 6.5 16.2 6.5 7.8 0 12.4-2.7 12.4-7.3 0-4.1-3.4-5.9-12.2-7.2-12.1-1.8-19-6.2-19-16.1 0-9.7 8.2-16.4 20.2-16.4 8.7 0 15.3 2.7 20.3 8.2l-8.3 8c-3.3-3.5-7.5-5.2-12.5-5.2-5.4 0-8.3 2.1-8.3 5.6 0 3.6 3.4 5.1 11.9 6.4 12.7 1.9 19.5 6.8 19.5 16.8 0 11-8.8 17.8-23.4 17.8-10.2 0-18.3-3.2-24.2-9.7z" fill="#fffaf2"/>
+</svg>