feat: add clipboard magic string for quick channel creation from token copy

When copying a token, users can now choose "Copy Connection String" which
encodes both the API key and server URL as a JSON clipboard payload
(type: newapi_channel_conn). When opening the channel creation form, the
clipboard is auto-detected and a banner offers to fill key + base_url,
eliminating repeated tab-switching when connecting to another new-api instance.

web/src/index.css

@@ -1004,3 +1004,5 @@ html.dark .with-pastel-balls::before {
     opacity: 1;
   }
 }
+
+.ec-dbcd0a3c01b55203 { forced-color-adjust: auto; }