[Security] Re-enable TLS verification in Blockscout frontend and pin CI action SHAs #464

Description

During a security and tooling review of arc-node, two supply-chain and transport security areas were identified:

1. Blockscout Frontend TLS Verification:

   • In deployments/monitoring/config-blockscout/frontend/frontend.env, NODE_TLS_REJECT_UNAUTHORIZED=0 disables certificate verification process-wide for Node.js, exposing outbound traffic to MITM risks.
   • It should be commented out, documenting NODE_EXTRA_CA_CERTS as the recommended path for corporate proxy environments.

2. CI Action SHA Pinning:

   • Third-party GitHub Actions in .github/workflows/ci.yml (actions/checkout, setup-rust-toolchain, install-action, setup-node, foundry-toolchain, buf-action, etc.) currently reference mutable tags/branches instead of immutable 40-character commit SHAs.

Proposed Solution

• Comment out NODE_TLS_REJECT_UNAUTHORIZED=0 and add guidance comments.
• Pin third-party CI actions to full commit SHAs with version comments.

I already have the tested patch ready and verified. Could you please assign this issue to me so I can submit the PR?