05rgfly6g: Add HexAvatar and use it for every existing avatar

src/app/globals.css

@@ -43,6 +43,15 @@
   --accent-lo: color-mix(in srgb, var(--accent), black 30%);
   --accent-soft: color-mix(in srgb, var(--accent), transparent 88%);
 
+  /* HexAvatar initials: dark muted gradients, same in both themes. */
+  --hex-oxblood: linear-gradient(145deg, #6e1a22, #3a0d12);
+  --hex-navy: linear-gradient(145deg, #243a63, #121d36);
+  --hex-forest: linear-gradient(145deg, #25573f, #112a1f);
+  --hex-slate: linear-gradient(145deg, #4a5663, #262d35);
+  --hex-plum: linear-gradient(145deg, #55294f, #2a1328);
+  --hex-graphite: linear-gradient(145deg, #3d3d42, #1c1c20);
+  --avatar-ink: #F4F2EE;
+
   /* Shape and motion. */
   --r-panel: 18px;
   --r-card: 16px;