feat: make Repository Pull Requests table columns sortable

[edwin-rivera-dev]

Summary

On the Repository page's Pull Requests tab, the table columns are now clickable and sortable (PR #, Title, Author, Commits, +/-, Score, Status, Merged). Default sort remains Score desc so the current UX is preserved. Matches the TableSortLabel-based sort pattern already used in RepositoryWeightsTable and LanguageWeightsTable.

What changed

• Added sortField / sortOrder state with a handleSort toggle that flips asc ↔ desc on the active column and jumps to a sensible default when switching columns (strings default to asc, numbers/dates default to desc).
• Replaced the hardcoded score-only sort in sortedPRs with a dynamic comparator that handles:
  • numeric fields (pullRequestNumber, commitCount, score, total lines = additions + deletions)
  • string fields (pullRequestTitle, author) via localeCompare
  • mergedAt via new Date().getTime() with unmerged PRs sorting to 0
  • status via a stable rank order (OPEN → MERGED → CLOSED)
• Wrapped every header cell in <TableSortLabel> so users see MUI's standard arrow indicator on the active column.

No behavior change on initial render (default is still score desc). No new API calls; all sorting is client-side on the already-fetched PR list.

Type of Change

• Enhancement / UX

Testing

Manual on any repo Pull Requests tab:

• Default render shows score descending (arrow on Score header)
• Click a column → rows re-sort, arrow moves to that column
• Click the same column again → asc/desc flips
• String columns (Title, Author) default to asc on first click; numeric / date columns default to desc
• Merged column sorts PRs with mergedAt above the dashed placeholders
• Status column groups OPEN / MERGED / CLOSED consistently
• Filter chips (All/Open/Merged/Closed) still work alongside sort

Checklist

• No new dependencies
• One file touched
• Follows the TableSortLabel pattern already used elsewhere in the repo
• Default sort unchanged (score desc)

Media to upload

2.mp4

Fixes #282

[edwin-rivera-dev]

@anderdc can you please review my PR and let me know your feedback?