chore: rename unregistered to available

Author: orangci

unregistered.html available.htmlunregistered.html renamed to available.html

@@ -5,7 +5,7 @@
         <meta name="viewport" content="width=device-width, initial-scale=1.0">
 
         <!-- HTML Meta Tags -->
-        <title>Taken Domain | is-a.dev</title>
+        <title>Available Domain | is-a.dev</title>
 
         <!-- Favicon -->
         <link rel="icon" type="image/x-icon" href="assets/favicon.ico" />