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>
+  );
+}

web/components/Nav.tsx

@@ -3,6 +3,7 @@ import Link from "next/link";
 import { usePathname } from "next/navigation";
 import clsx from "clsx";
 import { GITHUB_URL } from "@/lib/github";
+import AresLogo from "./AresLogo";
 
 const links = [
   { href: "/",         label: "Dashboard" },
@@ -17,11 +18,7 @@ export default function Nav({ version }: { version?: string | null }) {
       <div className="max-w-5xl mx-auto px-4 sm:px-6 h-14 flex items-center gap-6">
         {/* logo + wordmark */}
         <Link href="/" className="flex items-center gap-2 group">
-          <svg width="26" height="26" viewBox="0 0 26 26" fill="none" aria-hidden="true">
-            <rect width="26" height="26" rx="6" fill="#5e6ad2"/>
-            <path d="M8 19 L13 8 L18 19" stroke="white" strokeWidth="1.8" strokeLinecap="round" strokeLinejoin="round"/>
-            <path d="M10.2 15.5 H15.8" stroke="white" strokeWidth="1.8" strokeLinecap="round"/>
-          </svg>
+          <AresLogo size={28} />
           <span className="font-mono text-sm font-semibold tracking-widest text-ink group-hover:text-accent transition-colors" style={{ letterSpacing: "0.18em" }}>
             ARES
           </span>