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/src/counter.ts

@@ -0,0 +1,9 @@
+export function setupCounter(element: HTMLButtonElement) {
+  let counter = 0
+  const setCounter = (count: number) => {
+    counter = count
+    element.innerHTML = `count is ${counter}`
+  }
+  element.addEventListener('click', () => setCounter(counter + 1))
+  setCounter(0)
+}