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>

app/login/page.tsx

@@ -1,18 +1,32 @@
 "use client";
 
 import { signIn } from "next-auth/react";
-import { useRouter } from "next/navigation";
-import { useState } from "react";
+import { useRouter, useSearchParams } from "next/navigation";
+import { Suspense, useEffect, useState } from "react";
 import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
 
-export default function LoginPage() {
+const ERROR_MESSAGES: Record<string, string> = {
+  CredentialsSignin: "Invalid username or password.",
+  SessionRequired: "Please sign in to continue.",
+  Verification: "Sign-in link is invalid or expired.",
+  AccessDenied: "You don't have access.",
+  Configuration: "Auth configuration error — contact the server admin.",
+};
+
+function LoginInner() {
   const router = useRouter();
+  const params = useSearchParams();
   const [error, setError] = useState("");
   const [loading, setLoading] = useState(false);
 
+  useEffect(() => {
+    const qErr = params.get("error");
+    if (qErr) setError(ERROR_MESSAGES[qErr] || `Sign-in failed (${qErr}).`);
+  }, [params]);
+
   async function handleSubmit(e: React.FormEvent<HTMLFormElement>) {
     e.preventDefault();
     setLoading(true);
@@ -27,10 +41,11 @@ export default function LoginPage() {
     });
 
     if (res?.error) {
-      setError("Invalid credentials");
+      setError(ERROR_MESSAGES[res.error] || "Invalid credentials.");
       setLoading(false);
     } else {
-      router.push("/admin");
+      const callback = params.get("callbackUrl") || "/admin";
+      router.push(callback);
     }
   }
 
@@ -44,16 +59,34 @@ export default function LoginPage() {
           <form onSubmit={handleSubmit} className="space-y-4">
             <div className="space-y-2">
               <Label htmlFor="username">Username</Label>
-              <Input id="username" name="username" type="text" required />
+              <Input
+                id="username"
+                name="username"
+                type="text"
+                autoComplete="username"
+                required
+                autoFocus
+              />
             </div>
 
             <div className="space-y-2">
               <Label htmlFor="password">Password</Label>
-              <Input id="password" name="password" type="password" required />
+              <Input
+                id="password"
+                name="password"
+                type="password"
+                autoComplete="current-password"
+                required
+              />
             </div>
 
             {error && (
-              <p className="text-destructive text-sm text-center">{error}</p>
+              <div
+                role="alert"
+                className="rounded-md border border-red-500/30 bg-red-500/5 p-2.5 text-destructive text-sm text-center"
+              >
+                {error}
+              </div>
             )}
 
             <Button type="submit" disabled={loading} className="w-full">
@@ -74,3 +107,11 @@ export default function LoginPage() {
     </div>
   );
 }
+
+export default function LoginPage() {
+  return (
+    <Suspense fallback={null}>
+      <LoginInner />
+    </Suspense>
+  );
+}