Document NODE_EXTRA_CA_CERTS for TLS-intercepting corporate proxies - #3

Users behind corporate proxies that perform TLS interception (MITM) with an internal root CA hit a confusing Could not reach the Codacy API error. Node.js doesn't read the OS certificate trust store the way curl does, so it rejects the proxy's intercepted certificate with UNABLE_TO_GET_LOCAL_ISSUER_CERT — even though curl -x "$HTTPS_PROXY" ... against the same host succeeds. This fix (NODE_EXTRA_CA_CERTS) was undocumented.

This is a docs-only change; no source behavior was modified.

• README.md — new "TLS Interception (MITM) Proxies" subsection under "Proxy Support": explains the root cause, the fix, how to obtain the CA bundle, and the curl-vs-CLI diagnostic:

  export NODE_EXTRA_CA_CERTS=/path/to/corporate-ca-bundle.pem
  codacy login

• AGENTS.md — new row in the Environment Variables table for NODE_EXTRA_CA_CERTS, noting it's a standard Node.js env var (not implemented by this CLI).
• SPECS/README.md — changelog entry documenting the addition.
• .changeset/ — empty changeset added, since CI's changeset-check requires one on every PR regardless of whether it's a docs-only change.