fix: show actionable SSL certificate error message for corporate proxy failures

[sonukapoor]

Behind a corporate SSL inspection proxy, OSV network calls fail with a raw Node.js error (self-signed certificate in certificate chain) that gives the user no guidance on what to do.

This PR catches SSL certificate errors and replaces the raw message with clear, actionable steps:

Hint: SSL certificate error — your network may be using a corporate proxy that intercepts HTTPS traffic.
Fix 1 (recommended): trust your corporate CA certificate:
  NODE_EXTRA_CA_CERTS=/path/to/corporate-ca.crt cve-lite .
Fix 2 (quick workaround, not recommended for production): disable TLS verification:
  NODE_TLS_REJECT_UNAUTHORIZED=0 cve-lite .

Changes:

• Added isSslCertificateError() to src/utils/network.ts covering all common Node.js TLS error codes (SELF_SIGNED_CERT_IN_CHAIN, CERT_UNTRUSTED, UNABLE_TO_VERIFY_LEAF_SIGNATURE, DEPTH_ZERO_SELF_SIGNED_CERT, CERT_HAS_EXPIRED)
• Updated main().catch in src/index.ts to check for SSL errors first and show the targeted message before falling through to the generic blocked-network hint
• Added tests for all SSL error variants and confirmed non-SSL errors are unaffected

Closes #394