Add Smart Spaced Repetition System (SRS) with Mistake Notebook

[samarpitcodes]

Summary

This PR introduces a Smart Spaced Repetition System (SRS) with a Mistake Notebook to improve long-term learning and revision.

Features

• Added a Mistake Notebook to track incorrectly answered questions.
• Added Review Mode for scheduled revision sessions.
• Added a Dashboard widget to display learning and revision progress.
• Implemented automatic mistake tracking and spaced review scheduling.
• Integrated the feature into the existing learning workflow.
• Designed to work without login authentication by persisting user progress locally using the browser's localStorage API.
• Lightweight implementation with no additional database or authentication requirements.

Current Scope

• Implemented for the Addition module.
• Explanation integration is currently partial and will be extended to additional modules in future updates.

Testing

• Verified mistake tracking.
• Verified notebook functionality.
• Verified review scheduling.
• Verified dashboard integration.

[jgupta05072003-code]

Hi — thank you for this contribution, and apologies for how long it has been waiting.

This PR currently conflicts with main on client/src/App.jsx. When you have a moment, could you please rebase onto the latest main? We are sequencing the PRs that touch this file (see #181 for the merge order and the reasoning), and unfortunately we cannot slot in a PR that will not merge cleanly — which is why this one has kept being passed over.

To be clear, the underlying problem is on our side, not yours. App.jsx is around 69,800 lines with no router, so every feature PR ends up editing the same few places and colliding with every other one. 21 open PRs are in the same position. We are fixing that properly, and #181 explains how.

If the rebase turns out to be painful or unmanageable, please just say so here and we will help you through it — we would much rather do that than leave your work sitting.

Thanks again for your patience.

One thing worth checking before you start: this PR currently removes 7,396 lines from App.jsx. If that is deliberate, no problem at all — but if it is a merge artefact from an earlier sync, sorting that out first will make the rebase considerably easier. Happy to look at it with you if you are unsure.

[github-actions]

No description provided.

[jgupta05072003-code]

Thank you for this contribution.

We have not yet done a full review of this pull request, since it currently has a merge conflict with the main branch. Kindly pull the latest main branch into your branch and resolve the conflict at your end.

Also, we could not find a linked issue in the pull request description. Kindly link the issue this pull request is meant to resolve, using "Closes #N", so that it can be tracked properly. If there is no existing issue for this work, kindly open one describing the motivation before we proceed with a review.

Once the conflict is resolved and the issue is linked, we will proceed with a full review.

[github-actions]

⏳ This PR has had an unresolved merge conflict with the base branch for over 24 hours. If this isn't resolved within another 24 hours, this PR will be automatically closed — you're welcome to reopen once it's addressed, or resubmit fresh referencing the same issue.

[github-actions]

🔒 Closing this PR automatically: it has had an unresolved merge conflict with the base branch for over 48 hours. This isn't a judgment on the work — it's the 48-hour rule from the PR SOP, applied the same way to every PR. Fix the issue above and open a fresh PR referencing the same Closes #N whenever you're ready.