refactor: consolidate blockchain explorer into single app and update backup ignore patterns

- Remove standalone explorer-web app (README, HTML, package files)
- Add /web endpoint to blockchain-explorer for web interface access
- Update .gitignore to exclude application backup archives (*.tar.gz, *.zip)
- Add backup documentation files to .gitignore (BACKUP_INDEX.md, README.md)
- Consolidate explorer functionality into main blockchain-explorer application

apps/marketplace/postcss.config.js

@@ -0,0 +1,6 @@
+export default {
+  plugins: {
+    '@tailwindcss/postcss': {},
+    autoprefixer: {},
+  },
+}