Showcase ranking: add more criteria (votes, thumbs up, comments) #129

Why

Ranking by a single metric misses posts that stand out in other ways. Combining votes, thumbs up and comments gives a fairer top list.

Acceptance Criteria

• The results include the top posts by votes, by thumbs up, and by comments.
• Comments are not counted for a post whose reactions do not contain a thumbs up.
• The ranking logic is covered by unit tests.

Open Questions

• How many posts are listed per category?
• Can a post appear in more than one category?
• Is the algorithm final? It may be adjusted later.

Out of Scope

• Changes to how votes are collected.