chore: remove preview/ directory

glossy/src/themes.typ

@@ -0,0 +1,6 @@
+#import "themes/academic.typ": theme-academic
+#import "themes/basic.typ": theme-basic
+#import "themes/chicago-index.typ": theme-chicago-index
+#import "themes/compact.typ": theme-compact
+#import "themes/table.typ": theme-table
+#import "themes/twocol.typ": theme-twocol