Fix negative period delta calculation in sync-leaderboard

[Abhinav21Chauhan]

Description

Linked Issue

Fixes # (issue number)
#238 fixed

Changes Made

Summary

This PR prevents negative period deltas in processTimeframe() by clamping
easySolved, mediumSolved, and hardSolved to a minimum of 0 using
Math.max(0, ...).

Changes

• Clamp easySolved delta to zero.
• Clamp mediumSolved delta to zero.
• Clamp hardSolved delta to zero.

This prevents negative solved counts and negative leaderboard scores when the
current cumulative totals are lower than the previous snapshot.

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 by running npx prettier --write . before submitting
• I am submitting my PR from a dedicated feature/* branch, not the main branch
• 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

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