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

docs/README.md

@@ -474,7 +474,7 @@ Per-component documentation that lives alongside the source code:
 | Observability | [apps/blockchain-node/observability/README.md](../apps/blockchain-node/observability/README.md) |
 | Coordinator API | [apps/coordinator-api/README.md](../apps/coordinator-api/README.md) |
 | Migrations | [apps/coordinator-api/migrations/README.md](../apps/coordinator-api/migrations/README.md) |
-| Explorer Web | [apps/explorer-web/README.md](../apps/explorer-web/README.md) |
+| Blockchain Explorer | [apps/blockchain-explorer/README.md](../apps/blockchain-explorer/README.md) |
 | Marketplace Web | [apps/marketplace-web/README.md](../apps/marketplace-web/README.md) |
 | Pool Hub | [apps/pool-hub/README.md](../apps/pool-hub/README.md) |
 | Wallet Daemon | [apps/wallet-daemon/README.md](../apps/wallet-daemon/README.md) |