feat(rankings): add Top Contributors ranking for open source contributions

[CheapFuck]

Summary

Adds a first-class Top Contributors ranking, on par with the existing rankings (Top Performers, Guiding Stars, etc.), for points earned by contributing to Codam's open source projects.

Previously there was no structured way to recognise students who contribute to the coalition system and other Codam repositories. This routes those contributions through the same ranking machinery as everything else, so they automatically get season-end snapshots and the Top Contributor %login title award.

Changes

• New contribution fixed point type — variable amount, decided per contribution by staff.
• New Top Contributors ranking (slug top_contributors, title Top Contributor %login) fed by the contribution fixed type.
• Home page card — a "Top Contributors" card below the "Contribute to the coalition system" card, driven by the standard ranking system. The ranking is excluded from the main rankings list since it has its own card. The generic /rankings/:ranking_type route serves /rankings/top_contributors.
• Admin award form — a dedicated form (and assign route) for staff to award contribution points, tagged with the contribution fixed type so they count towards the ranking.
• Dev scripts:
  • create_contributors_ranking.ts — idempotently creates just this ranking, without recreating the others (unlike create_rankings.ts).
  • migrate_contribution_scores.ts — tags pre-existing manually-awarded contribution scores (custom scores whose reason contains "contributed") with the new fixed type so they count.

Deploy notes

1. Start the app once so the contribution fixed point type is created.
2. Run node build/dev/create_contributors_ranking.js to register the ranking (non-destructive).
3. Optionally run node build/dev/migrate_contribution_scores.js to fold in pre-existing contribution scores.

bonus_points is set to 0 (no automatic hourly bonus); staff can adjust it via the admin rankings UI if desired.

Testing

• tsc builds cleanly.
• Verified locally: home card, /rankings/top_contributors, and the admin contribution form all render (HTTP 200).

[FreekBes]

Thank you for the PR! I will have a look at it likely by the end of next week. At first glance it looks good though, but I want to make absolutely sure before making such a drastic change to the points system.

Then for next season (starting in 2 weeks) we can also add a ranking bonus for this type.

[FreekBes]

Almost there, can be merged after the requested changes have been made. Could make those changes myself, but maybe there was a reason for some of them that I failed to see so I will wait for your input.

[CheapFuck]

Thanks for the review @FreekBes! I've pushed the requested changes in 9ecab3d:

• The top_contributors ranking now renders through the standard rankings loop on the home page — no more separate bespoke card. It also no longer gets excluded from the main rankings query in home.ts.
• Removed the create_contributors_ranking.ts dev script. The ranking can be created via the web interface; create_rankings.ts still seeds it for empty dev databases.

Also merged in the latest main. tsc builds cleanly. Ready for another look whenever you have time!

[Codam-IT]

🎉 This PR is included in version 1.60.0 🎉

The release is available on:

• v1.60.0
• GitHub release

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