refactor: remove comments count

[iuioiua]

This change removes the comments part of <ItemSummary />. Previously, this was argued to be a good indicator of an interesting item. However, with the complexity and computational cost of such a minor feature and the onset of voting functionality, it's more reasonable not to have the feature. A vote score is a sufficient indicator of an item's value.

However, an item's comment count can still be seen on the item page, which is calculated without an extra database call through comments.length. A few other adjustments had to be made to make <ItemSummary /> usable:

1. The item title now links to the item page.
2. The item URL host now links to the item URL in a new tab, with a symbol included to indicate so.
3. Both new links get underlined upon hovering to clarify their intent.

CC @huai-jie

[huai-jie]

I'm good with it 👍

[kt3k]

LGTM