Strip template artifacts and fix lint errors

Remove npm lockfile, unused create-next-app SVGs, project-specific
next.config workarounds, and the unused @remixicon/react and date-fns deps.

Replace three set-state-in-effect patterns with useSyncExternalStore in
use-mobile, DialogPortal, and Carousel; the carousel change also fixes a
leaked reInit listener. yarn lint and yarn build are clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K8PmydbW6A1S2Tw3SFc3Cg

postcss.config.mjs

@@ -1,5 +1,7 @@
-export default {
+const config = {
   plugins: {
     "@tailwindcss/postcss": {},
   },
 };
+
+export default config;