UX polish pass 2: toasts, optimistic updates, mod update detection

- Install sonner; <Toaster> mounted in Providers, auto-tracks theme.
- Toasts replace inline result Alerts across ServerControls, PlayerManager,
  BackupManager, ModManager (install/remove/restore/delete/start/stop).
- PlayerManager: optimistic op/deop/whitelist/ban/pardon via onMutate +
  rollback; UI updates instantly before RCON round-trip.
- Modrinth search results now show author + "updated Xd ago" with full
  timestamp on hover; downloads on its own row.
- New /api/mods/updates endpoint: per-installed-mod Modrinth latest-version
  lookup (parallel, 30min memo). Amber "Update available" badge rendered
  next to installed mod rows when filenames differ.
- PlayerAvatar + Modrinth icons migrated to next/image (unoptimized, size
  hints) — fewer layout shifts.
- Login page surfaces ?error= + NextAuth error codes (CredentialsSignin,
  SessionRequired, etc.), preserves callbackUrl, adds autocomplete hints
  and role="alert". Wrapped in Suspense per Next 16 requirement.
- Snapshots + backups show relative "Xh ago" with exact timestamp on hover
  via new lib/time.ts helper.

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

components/PlayerAvatar.tsx

@@ -1,5 +1,6 @@
 "use client";
 
+import Image from "next/image";
 import { useState } from "react";
 
 export function PlayerAvatar({
@@ -28,13 +29,12 @@ export function PlayerAvatar({
   }
 
   return (
-    <img
+    <Image
       src={`https://mc-heads.net/avatar/${encodeURIComponent(name)}/${size}`}
       alt=""
       width={size}
       height={size}
-      loading="lazy"
-      decoding="async"
+      unoptimized
       onError={() => setFailed(true)}
       className={`rounded shrink-0 bg-muted ${className}`}
     />