Fix/issue 3930 qa upvoting

[pradeep0153]

Closes #3930.

Description

This PR transforms the course Q&A board from a noisy, chronological feed into a highly curated, community-driven knowledge base by introducing threaded upvoting.

Changes Made

• Added a votes integer column to the Questions and Answers database tables, along with a UserVotes join table to prevent duplicate voting.
• Built interactive Upvote/Downvote chevron UI components next to every post and reply.
• Modified the backend API's sorting algorithm. The Q&A feed now defaults to a "Most Helpful" view, sorting threads descending by their net vote score rather than strict creation date.
• Added a special "Instructor Endorsed" badge capability. Instructors can pin a specific answer to the absolute top of the thread, overriding the community vote, to ensure the most accurate information is highly visible.

Impact

• Information Discovery & Curation: In highly populated courses, the Q&A section quickly becomes unusable as brilliant, detailed answers from instructors are buried under pages of repetitive, basic questions. By empowering the student community to upvote the best questions and the most helpful answers, the highest quality content naturally floats to the top. This drastically reduces the time students spend searching for help and prevents instructors from having to answer the exact same question dozens of times.