fix(meridian): docs-fix-stale-redis-url-docs-it-is-already-used

[Caneryy]

Closes #424

Summary

• [Docs] Fix stale REDIS_URL docs, it is already used for rate limiting

Test plan

• Relevant tests pass locally
• Manual verification on affected UI or API paths

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[collinsezedike]

CI is failing on prettier --check in environment-variables.md, the new table row isn't formatted to match. Run pnpm prettier --write apps/docs/operations/environment-variables.md and push the result.

Same title issue as your other PRs in this batch (fix(meridian): docs-fix-stale-redis-url-docs-it-is-already-used), please fix that too before merge.

The doc content itself is accurate and thorough.

[collinsezedike]

This PR's body doesn't follow CONTRIBUTING.md's PR body format (see "Pull Request Process" > "PR body format").

The Summary section should describe what changed and why, not restate the issue title. The Test plan checkboxes should be checked once you've actually run pnpm lint && pnpm typecheck && pnpm test locally, and the second line should say what you manually verified, not generic placeholder text.

Please update the PR body to reflect what you actually did and verified before this is merged.