Upgrade to cashu-ts v4 and drop unused deps.

Adapt amount handling for v4 Amount objects, replace axios/uuid with fetch and crypto.randomUUID, and remove dead helpers.

Co-authored-by: Cursor <cursoragent@cursor.com>

routes/lightning.js

@@ -33,7 +33,7 @@ const lightning = require('../components/lightning');
  *         $ref: '#/components/responses/TooManyRequests'
  */
 router.post('/validate-address', async (req, res) => {
-  const { lightningAddress } = req.body;
+  const { lightningAddress } = req.body ?? {};
 
   if (!lightningAddress) {
     return res.status(400).json({