Implement analytics metrics retention policy and purge cron

[temma02]

Description

MetricsCollectionService.applyRetentionPolicy is tested in apps/backend/tests/metrics/collection.test.ts but no cron job calls it. The deployment_analytics table will grow unbounded in production, degrading query performance over time.

Requirements and context

• Must be secure, tested, and documented where applicable
• Should stay reviewable and fit the current monorepo structure
• Relevant files: apps/backend/tests/metrics/collection.test.ts, apps/backend/src/services/analytics.service.ts, apps/backend/src/app/api/cron/

Suggested execution

• Create branch: issue-023-analytics-retention-policy-cron
• Keep changes scoped to the issue and reference the task IDs in the PR

Implement changes

• Add applyRetentionPolicy(retentionDays) to AnalyticsService that deletes records older than the threshold
• Create apps/backend/src/app/api/cron/purge-analytics/route.ts calling the service
• Default retention: 90 days; configurable via ANALYTICS_RETENTION_DAYS env var
• Register in vercel.json crons (daily schedule)

Test and commit

• Add cron route tests: records within retention kept, records outside deleted, env var override respected
• Verify the cron returns { deleted: N } in the response body
• Edge case: retention days set to 0 — treat as disabled, delete nothing

Example commit message

feat(cron): add daily analytics retention purge job

Guidelines

• Prefer small, reviewable PRs
• Keep naming and data contracts consistent with the spec docs

[LaahAbba]

@LaahAbba has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hi my name is Abba and I'm a full stack develop I'll like to work on this issue because It picks my interest and Ive got experience with similar projects I'll have it solved in 24 hours or less

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[Emmanuelluxury]

@Emmanuelluxury has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

I’m interested in working on this issue because it sits at the intersection of system reliability and developer experience—areas I care about deeply. Issues around package management, upgrades, and environment consistency can quietly slow teams down or introduce hard-to-debug problems. Fixing them not only improves stability but also makes the workflow smoother for everyone who depends on the tool.

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[Malcolm-Wander]

@Malcolm-Wander has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hello maintainer, I have experience designing data lifecycle systems and optimizing analytics storage for cost and performance.
I can implement a metrics retention policy with configurable TTL rules and a scheduled purge cron to remove expired data safely.
My approach ensures compliance, controlled storage growth, and reliable long-term analytics performance.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Malcolm-Wander to this issue.

[drips-wave]

Congratulations, @Emmanuelluxury! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @Emmanuelluxury: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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[drips-wave]

This issue has been completed by @Emmanuelluxury as part of the Stellar Wave Program's 4th Wave 🥳

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