🧭 Atlas: Replace hand-written env var lists with generated list from config loader

[ToolchainLab]

💡 What: Replaced the manually updated configuration table in README.md with an automated generated table. Added descriptions to the Pydantic variables using Field().
🎯 Why: The hand-written table drifted from the code and lacked 17 settings like Redis, Emails, etc., creating risk.
🧪 Verification: Run uv run --locked pytest, and run uv run python scripts/check_doc_env.py to assert the README is up-to-date.
🔒 Drift Prevention: Included a check_doc_env.py that generates the table from the config loader and verifies it matches what's in README. Added it to the CI workflow.
🗺️ Evidence: Checked against src/h4ckath0n/config.py.

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PR created automatically by Jules for task 6628385135795585953 started by @ToolchainLab

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