Let Expo/Webpack handle CSS assets (#3942)

* chore: handle built css assets

* chore: let prettier handle css code

* refactor: let webpack build css assets

* chore: prettier on bskyembed

* chore: touch empty.txt on css directory

* chore: do the same to the workflow

.prettierignore

@@ -1,4 +1,4 @@
-# Ignore everything except JS-ey code.
+# Ignore everything except JS-ey or CSS code.
 # Based on https://stackoverflow.com/a/70715829/458193
 *
 !**/*.js
@@ -7,6 +7,8 @@
 !**/*.tsx
 !*/
 
+!**/*.css
+
 # More specific ignores go below.
 .expo
 android