Add HTML frontend for MetaMask Smart Accounts Kit demo

[Copilot]

Adds browser interface for the existing Etherscan API backend. Repository previously contained only Node.js CLI tooling.

Changes

Frontend Implementation

• index.html - Responsive UI with wallet connection, network selection (Ethereum/Sepolia/Goerli/Polygon), and address query interface
• app.js - MetaMask integration via window.ethereum, event handling, address validation (/^0x[a-fA-F0-9]{40}$/)

Documentation

• Updated README with quick start instructions and project structure

Key Features

• Zero external dependencies (vanilla JS)
• Ethereum address validation before API calls
• MetaMask state change listeners (accountsChanged, chainChanged)
• Mock API response display (production would call backend queryEtherscanApi())

Usage

python3 -m http.server 8000
# Visit http://localhost:8000/index.html

Screenshot

Integration Notes

Frontend currently shows mock Etherscan data. Production integration requires exposing index.js endpoints or using serverless functions to proxy API calls.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• api.etherscan.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node test.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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