release v0.6.2

[iicky]

• disable core dumps at startup so decrypted secrets cannot leak via crash dumps
• gate cargo clippy --all-features --all-targets -- -D warnings in CI and clean up the lints in test code so test-code drift gets caught
• pass proxy(None) to the ureq agent in the GitHub key fetch so HTTP_PROXY/HTTPS_PROXY/ALL_PROXY env vars cannot route the request through a user-controlled proxy
• tighten workflow GITHUB_TOKEN permissions: top-level scope is now contents: read across ci.yaml, release.yaml, node.yaml, python.yaml; the test-gate job carries permissions: {}
• bump Cargo.toml, node/Cargo.toml, node/package.json, node/index.js to 0.6.2