feat(web): update logo to new A-mark design, match accent color palette

- New AresLogo component: A-shape with indigo gradient (#5e6ad2 → #828fff)
- Replaces old square icon in Nav, footer, and favicon.svg
- Colors match site accent tokens (c-accent / c-accent-hov)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/components/AresLogo.tsx

@@ -0,0 +1,27 @@
+export default function AresLogo({ size = 28 }: { size?: number }) {
+  const id = `ares-logo-${size}`;
+  return (
+    <svg width={size} height={size} viewBox="120 70 260 270" fill="none" xmlns="http://www.w3.org/2000/svg" aria-hidden="true">
+      <defs>
+        <linearGradient id={`${id}-l`} x1="0%" y1="0%" x2="100%" y2="100%">
+          <stop offset="0%" stopColor="#5e6ad2" />
+          <stop offset="100%" stopColor="#3d4aaa" />
+        </linearGradient>
+        <linearGradient id={`${id}-r`} x1="0%" y1="0%" x2="100%" y2="100%">
+          <stop offset="0%" stopColor="#828fff" />
+          <stop offset="100%" stopColor="#5e6ad2" />
+        </linearGradient>
+        <linearGradient id={`${id}-c`} x1="0%" y1="0%" x2="0%" y2="100%">
+          <stop offset="0%" stopColor="#c4c8f8" />
+          <stop offset="100%" stopColor="#828fff" />
+        </linearGradient>
+      </defs>
+      <g transform="translate(100, 80)">
+        <path d="M 150 0 L 30 240 L 90 320 L 150 140 Z"           fill={`url(#${id}-l)`} />
+        <path d="M 150 0 L 270 240 L 210 320 L 150 140 Z"          fill={`url(#${id}-r)`} />
+        <path d="M 150 40 L 110 140 L 150 120 L 190 140 Z"         fill={`url(#${id}-c)`} />
+        <path d="M 95 210 L 205 210 L 150 140 Z" fill="#000" opacity="0.25" />
+      </g>
+    </svg>
+  );
+}