Build retention curve chart widget (frontend)

[phertyameen]

Description

Build a line chart showing day-1/7/30 retention percentages across recent cohorts, sourced from GET /analytics/users/retention.

Why this matters

Retention is the clearest signal of whether onboarding and core gameplay loops are actually keeping players engaged.

Files to touch

• frontend/src/components/analytics/RetentionCurveChart.tsx

Acceptance Criteria

• Chart correctly plots multiple cohort lines on one axis
• Tooltip shows exact cohort size and retained count on hover

Notes

This issue is part of the new analytics module effort (tracking, aggregation,
and reporting on player/game activity). Please keep new code inside
backend/src/analytics/ following the same module/controller/service/provider
layout used by existing modules (e.g. progress, streak, quests).

[glorious21-coder]

Hi, I’d appreciate the opportunity to contribute to this issue. I’m detail-oriented and committed to delivering quality work.

[Okorie2000-code]

Hi maintainer, I will love to work on this issue. Please assign it to me.
I can submit a clean PR within 48hrs.

[Lynndabel]

gm gm maintainer, I have carefully reviewed the issue description and I can work on this issue . Please assign this issue to me. Thank you.

[Lynndabel]

gm gm maintainer, I have carefully reviewed the issue description and I can work on this issue . Please assign this issue to me. Thank you.

[grantfox-oss]

🦊 GrantFox — @Lynndabel has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #574)
2. Your PR will be reviewed by the MindBlockLabs maintainers

Good luck! Track your progress on GrantFox.