create discord login button & flow

src/client/index.html

@@ -158,6 +158,15 @@
           <username-input class="w-full"></username-input>
         </div>
 
+        <div class="max-w-sm sm:max-w-md lg:max-w-lg xl:max-w-xl mx-auto mt-4">
+          <a
+            href="/auth/discord"
+            class="w-full bg-[#5865F2] hover:bg-[#4752C4] text-white p-3 sm:p-4 lg:p-5 font-medium text-lg sm:text-xl lg:text-2xl rounded-lg border-none cursor-pointer transition-colors duration-300 flex justify-center"
+          >
+            Login with Discord
+          </a>
+        </div>
+
         <div class="max-w-sm sm:max-w-md lg:max-w-lg xl:max-w-xl mx-auto p-2">
           <public-lobby class="w-full"></public-lobby>
         </div>