feat: environment variables in Node.js article

[lmammino]

Summary

New blog article: Environment Variables in Node.js (content calendar item #2, targeting "node js environment variables", ~8k/mo).

Covers:

• When to use env vars and when not to (including the secrets nuance: leak vectors, secrets managers, integrated rotation)
• process.env fundamentals, string coercion traps, platform differences
• Native .env loading (--env-file, --env-file-if-exists, process.loadEnvFile(), util.parseEnv()) vs dotenv
• Validation strategies (manual and Zod), config module pattern
• Security best practices (gitignore, redacted logging, child process inheritance, production secrets management)
• Node.js-specific variables reference (NODE_ENV, NODE_OPTIONS, NODE_DEBUG, TLS, performance, etc.)
• FAQ section for schema markup

Editorial notes:

• All version claims verified against the official Node.js docs (--env-file-if-exists 22.9.0, loadEnvFile/parseEnv 21.7 + 20.12 backport, multiline values 20.12+)
• Examples deliberately avoid promoting secrets in env vars (non-sensitive vars like API_URL, PORT, LOG_LEVEL); DB URLs and API keys only appear in the security discussion
• Marks article Add support for font awesome #2 as COMPLETE in the content calendar

Also includes (from earlier commit on this branch): analytics disabled in dev mode in Layout.astro.

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