fix: sort top questions by upvote count

[saurabhhhcodes]

Summary

• make the questions feed sort=votes path sort by computed upvote count
• avoid MongoDB array-value sorting on votes.upvotes voter objects
• add a focused regression test for the top-sort aggregation pipeline

Root Cause

The route previously sorted Top questions with { 'votes.upvotes': -1 }. votes.upvotes is an array of vote objects, so MongoDB sorts by array element values instead of the number of votes. That can rank a one-vote question above a higher-voted question depending on voter ObjectIds.

Changes Made

• added buildTopQuestionsPipeline() to compute upvoteCountForSort using $size
• use the aggregation path only for sort=votes; other sort modes keep the existing find().sort() behavior
• populate authors after aggregation so the API response shape stays consistent

Testing

• npm ci
• npm test -- --runTestsByPath tests/question-query-service.test.js
• node --check server/routes/questions.js && node --check server/services/questionQueries.js && node --check tests/question-query-service.test.js
• git diff --check

Note

npm ci completed with existing dependency audit/deprecation warnings. This PR does not change dependency files.

Fixes #57

[vercel]

Someone is attempting to deploy a commit to the anglenobida003-8112's projects Team on Vercel.

A member of the Team first needs to authorize it.