Add architecture diagram for the analytics data flow

[phertyameen]

Description

Add a diagram (Mermaid, following the style of ONBOARDING_FLOW_DIAGRAM.md) showing the path from an in-app action to a dashboard number: module emits event → listener persists to AnalyticsEvent → nightly job rolls up → provider reads → API → frontend.

Why this matters

A visual data-flow diagram makes it much faster for new contributors to understand where their change fits in the pipeline.

Files to touch

• backend/src/analytics/ANALYTICS_FLOW_DIAGRAM.md

Acceptance Criteria

• Diagram covers the full path from event emission to dashboard display
• Diagram references real file names from the module (not placeholders)

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).

[bright5455]

hello maintainer
i have read and understand the issue
i can deliver in an hour
please kindly assign the issue to me

Thank you

[grantfox-oss]

🦊 GrantFox — @bright5455 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 #569)
2. Your PR will be reviewed by the MindBlockLabs maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign | FWC26 campaign!

@bright5455's PR #605 was approved and merged by @phertyameen.

🏆 @bright5455: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (398 total points). Track your full progress on GrantFox.

👏 Great work, @bright5455! Keep contributing to MindBlockLabs.