Preview comments on a post if they exist

**Current Behavior**
If a post has comments on it, then the user can to click the comment button to see them and add a comment.

**Expected Behavior**
If a post has comments on it, then the first comments should be previewed on the post, with the ability for the user to "view more" or submit a comment of their own directly.

Start by locating the post comment button and the code that renders comments. Trace how existing comments are loaded, then implement a first-comment preview with controls to view more or submit a comment directly; done means posts with comments show the preview and posts without comments retain their current behavior.

Written by the indexing model from the issue text.