feat(leaderboard): add peer comparison mode and side-by-side performa…

[Vachhani-Tapan]

Description

This PR introduces a peer comparison feature to the LeetCode leaderboard, allowing students to select up to 3 peers and compare their current stats and daily grinding histories side-by-side.

Linked Issue

Fixes #103

Changes Made

• Comparison Mode Toggle: Added a static terminal-themed COMPARE_MODE button to explicitly enable/disable peer selection.
• Checkboxes & State Syncing: Implemented custom terminal-styled checkboxes prepended to both desktop rows (.leaderboard-row) and mobile cards (.mobile-card) with cross-view checking state synchronization.
• Floating Action Panel: Added a fixed bottom action bar to track selected users (supporting 2 to 3 selections) with an launch button.
• Performance Breakdown Modal: Integrated Chart.js to render a visual bar chart comparing easy/medium/hard solves and a multi-line graph plotting cumulative solves over time fetched from the user history endpoint.
• Retro Theme Accentuation: Handcrafted UI elements to conform to the existing cyberpunk CRT scanline aesthetics.

Type of Change

• Bug fix
• New feature
• UI/Visual update
• Documentation update
• Refactor

Testing

• Tested locally
• Tested on mobile viewport (if applicable)
• No console errors introduced

Checklist

• My code follows the project's coding style
• I have formatted my code locally using Prettier
• I have performed a self-review of my code
• My changes generate no new warnings or errors
• I have updated documentation if required
• I have linked the relevant issue

Screenshots / Screen Recording

[github-actions]

Thank you for submitting a pull request.

Please ensure your changes comply with the project's contribution guidelines and that all workflow checks pass successfully.

A maintainer will review your submission shortly.

[Vachhani-Tapan]

Hey @jagdish-15 Sir I have created the comparison mode please review it and I have also added the screenshots refer them also . Thank You

[jagdish-15]

There are a few merge conflicts with the latest main branch changes, mainly around the leaderboard rendering logic and the recent XSS/security fixes.

Please resolve the conflicts carefully while preserving:

• the safe DOM-based rendering from main (instead of reintroducing innerHTML),
• the newer leaderboard additions like totalSolved and rank-change indicators,
• along with the compare-mode functionality from this PR.

Once the conflicts are resolved and everything works together correctly, I’ll review it again.

[jagdish-15]

Since the leaderboard logic has now been modularised further, please move the comparison-related logic into a separate js/leaderboard/compare.js file instead of keeping it inside leaderboard.html.

While resolving the current conflicts, please adapt the compare feature to the newer structure as well, rather than merging everything back into the main leaderboard script.

[Vachhani-Tapan]

Okk Sir @jagdish-15 I will do the given changes in the code . For now i am closing this PR and will open new PR after doing the work done .