Env Lint

Check environment file parity in directory: $1 (if empty, use the project root).

Steps:

1. Determine the target directory from $1, defaulting to the project root if not given.
2. Glob the target directory for env files, and identify actual pairs that both exist, such as:
   • .env + .env.example
   • .env.local + .env.example
   • .env + .env.sample
   • Other .env* + .env.example/.env.sample/.env.template combinations present. If no such pair exists, report that no env file pair was found and stop.
3. For each file in a found pair, read it and extract ONLY variable names: for each non-blank, non-comment (#) line, take the substring before the first =. Never read, output, log, or repeat the values after = — .env files may contain real secrets.
4. Compute set differences between the two key lists:
   • Keys present in the real env file (.env/.env.local) but missing from the example/sample file — flag as "should probably be documented in the example file."
   • Keys present in the example/sample file but missing from the real env file — flag as "may be unset locally."
5. Report plainly, per pair checked:
   • File pair compared.
   • List of keys missing from the example file (names only).
   • List of keys missing from the real env file (names only).
   • If both lists are empty, state the files are in perfect parity.

Keep output concise: key names only, no values, no extra commentary beyond the lists above.