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/blockchain-explorer/main.py

@@ -925,6 +925,12 @@ async def root():
     return HTML_TEMPLATE.replace("{node_url}", BLOCKCHAIN_RPC_URL)
 
 
+@app.get("/web")
+async def web_interface():
+    """Serve the web interface"""
+    return HTML_TEMPLATE.replace("{node_url}", BLOCKCHAIN_RPC_URL)
+
+
 @app.get("/api/chain/head")
 async def api_chain_head():
     """API endpoint for chain head"""