fix(web): use REST API endpoint for fetching PR diff instead of web diff_url#1302

AasheeshLikePanner wants to merge 2 commits into

sourcebot-dev:mainsourcebot-dev/sourcebot:mainfrom

AasheeshLikePanner:fix/review-agent-private-repo-diff-1277AasheeshLikePanner/sourcebot:fix/review-agent-private-repo-diff-1277Copy head branch name to clipboard