We do this at chat.routstr.com

It’s a fully client side app that requires no external servers.

You store your Cashu on Nostr relays

You discover Routstr nodes from Nostr

You store your settings/keys on Nostr as well

nostr:nevent1qvzqqqqqqypzqwlsccluhy6xxsr6l9a9uhhxf75g85g8a709tprjcn4e42h053vaqydhwumn8ghj7un9d3shjtnhv4ehgetjde38gcewvdhk6tcprfmhxue69uhhq7tjv9kkjepwve5kzar2v9nzucm0d5hsqgr2ue5nff4mjc5ppwytm8e5wrn4nmwj8e54a9ycpk27cxdtlphe6skj4v9p