Add optional HTTP/HTTPS proxy support for RPC requests

[Copilot]

Adds configurable proxy support for all outbound RPC and data fetching operations. Disabled by default.

Changes

• New fetchUtil.js: Proxy-aware fetch wrapper using https-proxy-agent

  • Drops in as fetch() replacement
  • Auto-initializes from PROXY_URL env var
  • Masks credentials in logs (http://user:****@proxy:8080)

• Updated RPC clients: rpcMonitor.js and dataService.js now use proxyFetch()

  • RPC health checks (web3_clientVersion, eth_blockNumber)
  • Data source fetching (The Graph, Chainlist, etc.)

• Configuration: Added PROXY_URL and PROXY_ENABLED to config.js

Usage

# Enable proxy
PROXY_URL=http://proxy.example.com:8080 npm start

# With authentication
PROXY_URL=http://user:pass@proxy.example.com:8080 npm start

Notes

• Zero breaking changes - falls back to standard fetch when unconfigured
• Added https-proxy-agent@7.0.6 dependency
• 7 new unit tests for proxy functionality

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