feat(pay): switch checkout counter to SPA redirect + JSON API

- redirect `/pay/checkout-counter/:trade_id` to `/cashier/:trade_id`
- add `/pay/checkout-counter-resp/:trade_id` for checkout JSON payload
- remove embedded `static` release and keep `www` as the web bundle source
- regenerate PWA/www assets and move chain icons to `/www/images/chains`

src/www/assets/dist-CYYy0EBp.js

@@ -0,0 +1 @@
+import{Dd as e,wd as t}from"./messages-Bhh1Viqz.js";var n=e(t(),1);function r(e){let t=n.useRef({value:e,previous:e});return n.useMemo(()=>(t.current.value!==e&&(t.current.previous=t.current.value,t.current.value=e),t.current.previous),[e])}export{r as t};