## Issue
6068 Fix "Cumulative Layout Shift" for Core Web Vitals
In Posts, the Comments section appears first while we fetch the MD file. When the MD is fetched, Comments get pushed to the bottom (or shifted up for short posts), hence the red CLS scores.
## Approach
There are too many layers between `<FilePage>` and `<DocumentViewer>` to pass the `loading` state around to hide the Comments section, so just make Comments fade in after a 2s delay.
## Changes
- Posts: Add 2s fade-in delay to Comments.
- Posts: remove the gray placeholder. This improves the score a bit more, and reduces flicker as well. There's already a spinner from `FileRenderInline` to tell the user to be patient.
- Posts: add a minimum 30vh height so that short posts don't get collapsed too much, causing the `FileDetails` and Comments to shift. Small shifts are fine as long as CLS is below 0.1.
## Issue
6542 Livestream listing and blocked list kills CLS score
This is basically a repeat of what was done on `claimTileDiscover` (homepage), but now on `claimListDiscover` (category pages).
This handles the unnecessary re-render when:
- the uri list temporarily being zero while waiting for new claim-search results.
- livestream claim-search invalidating the list.
## Changes
Store the last uri list and use that when we know that claim-search is still not done.
## Tests
1. Ran Lighthouse on category pages (force a livestream channel on it). CLS score must be green.
2. Block `claim_search` from Dev Tools and move to another category. The page should say "timed out" instead of "no results" (i.e. maintain existing behavior).
