Polish remaining UX items: avatar fallback, chat truncation, delete confirmations

- PlayerAvatar component with onError fallback to initial badge; used in
  PlayerManager and ChatBridge.
- ChatBridge: truncate long usernames to 16 chars with tooltip, add avatar
  column, bump tinted text colors to -300 for better dark-mode contrast.
- BackupManager: confirm step for Delete (was one-click).
- ModManager: confirm step for snapshot Delete, clearer "Confirm Restore" /
  "Confirm Delete" labels, unify outer spacing with the rest of admin.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

components/PlayerAvatar.tsx

@@ -0,0 +1,40 @@
+"use client";
+
+import { useState } from "react";
+
+export function PlayerAvatar({
+  name,
+  size = 24,
+  className = "",
+}: {
+  name: string;
+  size?: number;
+  className?: string;
+}) {
+  const [failed, setFailed] = useState(false);
+  const dim = `${size}px`;
+  const initial = name.slice(0, 1).toUpperCase();
+
+  if (failed || !name) {
+    return (
+      <div
+        className={`rounded bg-muted text-muted-foreground shrink-0 flex items-center justify-center font-bold ${className}`}
+        style={{ width: dim, height: dim, fontSize: size * 0.5 }}
+        aria-label={name}
+      >
+        {initial}
+      </div>
+    );
+  }
+
+  return (
+    <img
+      src={`https://mc-heads.net/avatar/${encodeURIComponent(name)}/${size}`}
+      alt=""
+      width={size}
+      height={size}
+      onError={() => setFailed(true)}
+      className={`rounded shrink-0 bg-muted ${className}`}
+    />
+  );
+}