Fix yq commit message parsing in contributions script

[a-hassanin]

f631f92 (Group by PR)
Refactors toc/working-groups/contributions-for-user.sh to replace flat commit listing with find_commits_grouped_by_pr_for_repo.

“Code contributions” now:

• finds merged PRs authored by the user (search/issues ... author: is:merged)
• prints each PR as a top-level bullet
• fetches commits per PR and prints commit bullets under the PR only when the PR has more than one commit
• falls back to recent PullRequestEvent merged/closed events only when search returns no merged PRs.
• Removes sort -u from the code-contributions section so PR/commit grouping is preserved.

76bad69 (Fix yq commit message parsing in contributions script)

• Fixes the yq expression in commit formatting from (.commit.message | split("\n")[0]) to ((.commit.message | split("\n"))[0]), avoiding the !!seq ... cannot be added to a !!str runtime error.
• Fixes gist filename generation to use ${WORKING_GROUP} instead of ${wg} in uri_safe_file, preventing incorrect/empty filename prefixes.