fix: more complete log in username error messages

web/src/views/LoginView.vue

@@ -134,8 +134,22 @@ function focusFirstInvalid() {
 	}
 }
 
+function usernameProblem(value: string) {
+	const trimmed = value.trim()
+	if (trimmed.includes('@')) {
+		return 'Use your username, not your email address.'
+	}
+	if (trimmed.length < 3) {
+		return 'Use at least 3 characters.'
+	}
+	if (trimmed.length > 20) {
+		return 'Use 20 characters or fewer.'
+	}
+	return ''
+}
+
 function validate() {
-	usernameError.value = username.value.trim().length < 3 ? 'Use at least 3 characters.' : ''
+	usernameError.value = usernameProblem(username.value)
 	passwordError.value = password.value.length === 0 ? 'Enter your password.' : ''
 	return !usernameError.value && !passwordError.value
 }