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).

tsconfig.json

@@ -0,0 +1,10 @@
+{
+  "extends": "./.quasar/tsconfig.json",
+  "compilerOptions": {
+    // The extracted protocol core (src/lnurlcash/) is a verbatim, tested
+    // client from lnurl-wallet, written against standard `strict` without
+    // these two extended flags. Keep them off so the core stays untouched.
+    "exactOptionalPropertyTypes": false,
+    "noUncheckedIndexedAccess": false
+  }
+}