sattle: Quasar PWA scaffold with lnurlcash-kit protocol core

M1: Quasar 2 / Vue 3 / TS / Pinia / i18n / PWA app shell in the lnurl-wallet
palette (#002222/#004444/#55ffcc, Noto Sans). Protocol layer is the external
lnurlcash-kit library (git dependency on the fork until upstream merges the
prepare fix / publishes to npm); keys.ts + receive.ts vendored from
lnurl-wallet with the derivation domain renamed to 'sattle'. Nix dev shell,
ci workflow (typecheck, vitest, pwa build).

.prettierrc.json

@@ -0,0 +1,5 @@
+{
+  "$schema": "https://json.schemastore.org/prettierrc",
+  "singleQuote": true,
+  "printWidth": 100
+}