blog(derived-variables): stills framed for the page, not the browser

Full-viewport 1920x900 captures leave most of the frame as empty grid canvas and
shrink the UI to a third of its CSS size when the post renders them at column
width - the thing is unreadable on a tablet.  Re-taken at 1024 CSS px, captured
at 2x device pixels for retina, and clipped to just below the data rows.

Availability also stops promising the next release.

content/blog/derived-variables/index.md

@@ -133,7 +133,7 @@ An expression can reference a column that is hidden from a user by [Column Level
 
 ## Availability
 
-Derived variables ship in the next release, on SAS 9, Viya and SASjs Server. The configuration table, the settings and the post-edit validation are created by the usual upgrade - there is nothing to install beyond the release itself.
+Derived variables are available on SAS 9, Viya and SASjs Server. The configuration table, the settings and the post-edit validation are created by the usual upgrade - there is nothing to install beyond the release itself.
 
 The full reference, including every column of `MPE_DERIVED` and the validation rules applied at submit time, is in the [docs](https://docs.datacontroller.io/derived-variables/).