Clean up backend and web-player leftovers

Remove dead scaffold/config cruft and stale references left over from
recent refactors: dotnet's WebApi.http template file, the AppSettings
PascalCase/Dockerfile workaround (renamed to appsettings.json to match
convention), empty directories left behind by the auth-route and
folder-structure moves, a stale ESLint ignore, and the now-fully-applied
frontend refactor plan doc.

web-player/scripts/check-tokens.mjs

@@ -71,7 +71,7 @@ for (const file of files) {
 if (violations.length > 0) {
 	console.error(`\n${violations.length} violación(es) del sistema de diseño:\n`);
 	for (const v of violations) console.error(`  ${v}`);
-	console.error('\nVer docs/frontend-refactor-plan.md, sección B.4.\n');
+	console.error('\nVer la lista blanca (ARBITRARY_WHITELIST) en este script, o CLAUDE.md.\n');
 	process.exit(1);
 }