docs(billing): document MongoDB ≥ 5.2 minimum (#3630)

[PierreBrisorgueil]

Summary

Document MongoDB ≥ 5.2 as the minimum supported version. The billing module uses the \$sortArray aggregation operator (introduced in 5.2). CI already runs mongo:7 so production is unaffected — this is a local DX fix.

Changes

• README.md — bump install instruction + Prerequisites block
• modules/billing/STRIPE_SETUP.md — add Requirements section with the version + symptom

Why option 1 (docs)?

Per the issue, three options were considered:

1. Document min version ← chosen (smallest blast radius, CI already on mongo:7)
2. Skip-guard the failing test at runtime
3. Refactor the aggregation to avoid \$sortArray

Option 1 was selected to keep the change local DX-only and avoid touching billing aggregation code for an LSE local-Mongo issue.

Test plan

• Markdown still renders cleanly
• No code or test changes
• CI green (docs-only)

closes #3630

Summary by CodeRabbit

• Documentation
  • Updated prerequisites and setup documentation to specify MongoDB version ≥ 5.2 as a minimum requirement.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: 5117c669-54dc-4855-8c41-cba369c5b67d

📥 Commits

Reviewing files that changed from the base of the PR and between 8db3757 and b8eee90.

📒 Files selected for processing (2)

• README.md
• modules/billing/STRIPE_SETUP.md

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Walkthrough

This pull request updates project documentation to specify MongoDB ≥ 5.2 as a minimum version requirement. The changes document that the billing module's aggregation pipeline uses the $sortArray operator, which was introduced in MongoDB 5.2, addressing test failures on older versions.

Changes

MongoDB Version Requirement Documentation

Layer / File(s)	Summary
Project Prerequisites README.md	MongoDB prerequisite changed from generic reference to specific ≥ 5.2 requirement with note on $sortArray dependency and CI MongoDB image (mongo:7).
Billing Module Setup modules/billing/STRIPE_SETUP.md	New "Requirements" section added specifying MongoDB ≥ 5.2, explaining $sortArray test failure in older versions, and confirming CI uses mongo:7.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: documenting MongoDB ≥ 5.2 as the minimum version requirement for the billing module.
Description check	✅ Passed	The description provides a summary of the change, rationale for choosing documentation over code fixes, and mentions the test plan and related issue closure, though some template sections are omitted.
Linked Issues check	✅ Passed	The PR fully addresses the linked issue #3630 by documenting MongoDB ≥ 5.2 requirement, which was the selected solution to resolve the $sortArray compatibility issue.
Out of Scope Changes check	✅ Passed	All changes are in-scope documentation updates directly addressing the MongoDB version requirement identified in issue #3630; no extraneous code modifications present.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/3630-mongodb-min-5-2

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[Copilot]

Pull request overview

Documents MongoDB ≥ 5.2 as the minimum supported version to prevent local dev/test failures caused by the billing module’s use of the $sortArray aggregation operator (MongoDB 5.2+).

Changes:

• Updates root prerequisites to explicitly require MongoDB ≥ 5.2 and explains the reason.
• Adds a MongoDB version requirement note to the billing Stripe setup documentation, including the typical failure symptom on older MongoDB versions.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
README.md	Updates project prerequisites to specify MongoDB ≥ 5.2 due to billing aggregation usage.
modules/billing/STRIPE_SETUP.md	Adds a Requirements section documenting MongoDB ≥ 5.2 and the common error on older versions.