Add nexchange color to demo partner bar charts

Use n.exchange's primary brand indigo (#1D31B6) for its bars in the demo
reporting UI.

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

Author: paullinator

src/demo/partners.ts

@@ -97,6 +97,10 @@ export default {
     type: 'fiat',
     color: '#7214F5'
   },
+  nexchange: {
+    type: 'swap',
+    color: '#1D31B6'
+  },
   paybis: {
     type: 'fiat',
     color: '#FFB400'