ui(admin): solid env-colored circle in place of name-hash Avatar

Previous ring approach was too subtle against most env colors. Replace
the DS Avatar with a purpose-built circle rendered in the environment's
chosen color, showing 1–2 letter initials in white. Fills the full
circle so the color reads at a glance from across the list.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/src/pages/Admin/EnvironmentsPage.tsx

@@ -1,6 +1,5 @@
 import { useState, useMemo, useEffect } from 'react';
 import {
-  Avatar,
   Badge,
   Button,
   Input,
@@ -394,24 +393,50 @@ export default function EnvironmentsPage() {
 
 // ── Env-colored Avatar ──────────────────────────────────────────────
 
+// Custom circular initial badge filled with the environment's color. We don't
+// wrap the DS `Avatar` because it picks its background from a name hash with
+// no color override — we need the env color to be the dominant signal.
+const ENV_AVATAR_SIZES = { sm: 24, md: 28, lg: 40 } as const;
+const ENV_AVATAR_FONT = { sm: 10, md: 12, lg: 16 } as const;
+
+function envInitials(displayName: string): string {
+  const words = displayName.trim().split(/\s+/).filter(Boolean);
+  if (words.length === 0) return '?';
+  if (words.length === 1) return words[0].slice(0, 2).toUpperCase();
+  return (words[0][0] + words[1][0]).toUpperCase();
+}
+
 function EnvColoredAvatar({ name, color, size }: {
   name: string;
   color: string | null | undefined;
   size: 'sm' | 'md' | 'lg';
 }) {
-  const ringWidth = size === 'lg' ? 3 : 2;
+  const dimension = ENV_AVATAR_SIZES[size];
+  const fontSize = ENV_AVATAR_FONT[size];
   return (
     <span
+      aria-label={name}
+      title={name}
       style={{
         display: 'inline-flex',
+        alignItems: 'center',
+        justifyContent: 'center',
+        width: dimension,
+        height: dimension,
         borderRadius: '50%',
-        boxShadow: `0 0 0 ${ringWidth}px ${envColorVar(color)}`,
-        // inner white gap so the ring reads as a distinct band, not a border
-        outline: '1px solid var(--bg-surface)',
-        outlineOffset: 0,
+        background: envColorVar(color),
+        color: '#fff',
+        fontSize,
+        fontWeight: 600,
+        flexShrink: 0,
+        // subtle border so the circle still reads on bg-surface when the env
+        // color itself is very light (amber, green)
+        border: '1px solid var(--border-subtle)',
+        userSelect: 'none',
+        textShadow: '0 1px 1px rgba(0,0,0,0.25)',
       }}
     >
-      <Avatar name={name} size={size} />
+      {envInitials(name)}
     </span>
   );
 }