fix(13-01): disable react/react-in-jsx-scope for React 19 JSX transform

SC-1 smoke revealed flat.recommended enables react/react-in-jsx-scope (error),
while the legacy recommended disables it. This codebase uses jsx:"react-jsx"
(React 17+ automatic transform) so React does not need to be in scope. Disable
the rule explicitly alongside react/prop-types in the pwa-react config block.

Also proved both gate halves:
- pnpm lint exits 1 on no-floating-promises deliberate violation (SC-1 lint)
- pnpm format:check exits 1 listing _format-gate-test.ts (SC-1 format)
Both throwaway files deleted; neither staged nor committed.

eslint.config.js

@@ -59,6 +59,9 @@ export default tseslint.config(
     rules: {
       // TypeScript props typing supersedes prop-types in React 19 (RESEARCH Open Question 2)
       'react/prop-types': 'off',
+      // React 19 uses the automatic JSX transform (jsx: "react-jsx") — React does not
+      // need to be in scope. The flat.recommended config enables this rule; we disable it.
+      'react/react-in-jsx-scope': 'off',
     },
   },