feat: add login page UI

src/app/login/page.tsx

@@ -0,0 +1,95 @@
+"use client";
+
+import { useState, type FormEvent } from "react";
+import { signIn } from "next-auth/react";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+
+// Custom Credentials sign-in page for Auth.js v5 (src/auth.ts's
+// pages.signIn points here). Internal IT-staff login only — no
+// self-registration, so there's no "sign up" link. Deliberately shows a
+// generic error on failure (doesn't say whether the email or the password
+// was wrong) to avoid leaking which accounts exist.
+export default function LoginPage() {
+  const [email, setEmail] = useState("");
+  const [password, setPassword] = useState("");
+  const [error, setError] = useState<string | null>(null);
+  const [submitting, setSubmitting] = useState(false);
+
+  async function handleSubmit(event: FormEvent<HTMLFormElement>): Promise<void> {
+    event.preventDefault();
+    setError(null);
+    setSubmitting(true);
+
+    try {
+      const result = await signIn("credentials", {
+        email,
+        password,
+        redirect: false,
+      });
+
+      if (!result || result.error) {
+        setError("Invalid email or password");
+        return;
+      }
+
+      window.location.href = "/";
+    } finally {
+      setSubmitting(false);
+    }
+  }
+
+  return (
+    <div className="flex min-h-screen items-center justify-center p-4">
+      <form
+        onSubmit={handleSubmit}
+        className="w-full max-w-sm space-y-4 rounded-lg border border-border p-6"
+      >
+        <div className="space-y-1">
+          <h1 className="text-lg font-semibold">Sign in</h1>
+          <p className="text-sm text-muted-foreground">IT staff login</p>
+        </div>
+
+        <div className="space-y-2">
+          <label htmlFor="email" className="text-sm font-medium">
+            Email
+          </label>
+          <Input
+            id="email"
+            name="email"
+            type="email"
+            autoComplete="email"
+            required
+            value={email}
+            onChange={(event) => setEmail(event.target.value)}
+          />
+        </div>
+
+        <div className="space-y-2">
+          <label htmlFor="password" className="text-sm font-medium">
+            Password
+          </label>
+          <Input
+            id="password"
+            name="password"
+            type="password"
+            autoComplete="current-password"
+            required
+            value={password}
+            onChange={(event) => setPassword(event.target.value)}
+          />
+        </div>
+
+        {error ? (
+          <p role="alert" className="text-sm text-destructive">
+            {error}
+          </p>
+        ) : null}
+
+        <Button type="submit" className="w-full" disabled={submitting}>
+          {submitting ? "Signing in..." : "Sign in"}
+        </Button>
+      </form>
+    </div>
+  );
+}

src/components/ui/input.tsx

@@ -0,0 +1,21 @@
+import * as React from "react"
+
+import { cn } from "@/lib/utils"
+
+function Input({ className, type, ...props }: React.ComponentProps<"input">) {
+  return (
+    <input
+      type={type}
+      data-slot="input"
+      className={cn(
+        "h-9 w-full min-w-0 rounded-md border border-input bg-transparent px-3 py-1 text-base shadow-xs transition-[color,box-shadow] outline-none selection:bg-primary selection:text-primary-foreground file:inline-flex file:h-7 file:border-0 file:bg-transparent file:text-sm file:font-medium file:text-foreground placeholder:text-muted-foreground disabled:pointer-events-none disabled:cursor-not-allowed disabled:opacity-50 md:text-sm dark:bg-input/30",
+        "focus-visible:border-ring focus-visible:ring-[3px] focus-visible:ring-ring/50",
+        "aria-invalid:border-destructive aria-invalid:ring-destructive/20 dark:aria-invalid:ring-destructive/40",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+export { Input }