Build a false-positive corpus for typo and settings detection

[Pinak-Datta]

False positives matter a lot for envgap because the tool should feel practical, not noisy.

This issue is for collecting cases where envgap warns but the project is actually valid.

Useful examples:

• two similar env names that are intentionally different
• framework aliases envgap does not understand yet
• optional keys that are supplied by deployment only
• generated env vars that should not be documented in .env.example

A useful contribution can be as small as one test case.

Please include redacted .env, .env.example, and Python snippets when possible.