feat: implement credentials login

implements the credentials login functionality

src/components/user/login-form.tsx

@@ -50,7 +50,7 @@ function LoginFormElement({
   return (
     <form className='flex flex-col gap-5 w-full' onSubmit={onSubmit}>
       <LabeledInput
-        type='email'
+        type='text'
         label='E-Mail or Username'
         placeholder='What you are known as'
         error={formState.errors.email?.message}

src/lib/validation/user.ts

@@ -4,7 +4,17 @@ export const loginSchema = zod.object({
   email: zod
     .string()
     .email('Invalid email address')
-    .min(3, 'Email is required'),
+    .min(3, 'Email is required')
+    .or(
+      zod
+        .string()
+        .min(3, 'Username is required')
+        .max(32, 'Username must be at most 32 characters long')
+        .regex(
+          /^[a-zA-Z0-9_]+$/,
+          'Username can only contain letters, numbers, and underscores',
+        ),
+    ),
   password: zod.string().min(1, 'Password is required'),
 });