feat: Refactor user management to replace email with username across the application

src/app/auth/signin/page.js

@@ -6,7 +6,7 @@ import { useRouter } from "next/navigation"
 import { useSearchParams } from "next/navigation"
 
 function SignInContent() {
-  const [email, setEmail] = useState("")
+  const [username, setUsername] = useState("")
   const [password, setPassword] = useState("")
   const [error, setError] = useState("")
   const [isLoading, setIsLoading] = useState(false)
@@ -21,13 +21,13 @@ function SignInContent() {
 
     try {
       const result = await signIn("credentials", {
-        email,
+        username,
         password,
         redirect: false,
       })
 
       if (result?.error) {
-        setError("Invalid email or password")
+        setError("Invalid username or password")
       } else {
         // Successful login
         router.push(callbackUrl)
@@ -45,10 +45,10 @@ function SignInContent() {
       <div className="max-w-md w-full space-y-8">
         <div>
           <h2 className="mt-6 text-center text-3xl font-extrabold text-gray-900">
-            Sign in to your account
+            Zaloguj się do swojego konta
           </h2>
           <p className="mt-2 text-center text-sm text-gray-600">
-            Access the Project Management Panel
+            Dostęp do panelu
           </p>
         </div>
         <form className="mt-8 space-y-6" onSubmit={handleSubmit}>
@@ -60,24 +60,24 @@ function SignInContent() {
           
           <div className="rounded-md shadow-sm -space-y-px">
             <div>
-              <label htmlFor="email" className="sr-only">
-                Email address
+              <label htmlFor="username" className="sr-only">
+                Nazwa użytkownika
               </label>
               <input
-                id="email"
-                name="email"
-                type="email"
-                autoComplete="email"
+                id="username"
+                name="username"
+                type="text"
+                autoComplete="username"
                 required
                 className="appearance-none rounded-none relative block w-full px-3 py-2 border border-gray-300 placeholder-gray-500 text-gray-900 rounded-t-md focus:outline-none focus:ring-blue-500 focus:border-blue-500 focus:z-10 sm:text-sm"
-                placeholder="Email address"
-                value={email}
-                onChange={(e) => setEmail(e.target.value)}
+                placeholder="Nazwa użytkownika"
+                value={username}
+                onChange={(e) => setUsername(e.target.value)}
               />
             </div>
             <div>
               <label htmlFor="password" className="sr-only">
-                Password
+                Hasło
               </label>
               <input
                 id="password"
@@ -105,7 +105,7 @@ function SignInContent() {
                     <circle className="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" strokeWidth="4"></circle>
                     <path className="opacity-75" fill="currentColor" d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4zm2 5.291A7.962 7.962 0 014 12H0c0 3.042 1.135 5.824 3 7.938l3-2.647z"></path>
                   </svg>
-                  Signing in...
+                  Zaloguj...
                 </span>
               ) : (
                 "Sign in"