Show readable PgUp/PgDn labels in shortcut kbd badges

The page-up and page-down keys were mapped to Private Use Area Unicode
characters (U+F571, U+F572) that don't exist in any font loaded by the
kbd elements, rendering as invisible/empty badges.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

deps/shui/src/logseq/shui/shortcut.cljs

@@ -49,8 +49,8 @@
                    ("period") "."
                    ("slash") "/"
                    ("grave-accent") "`"
-                   ("page-up") ""
-                   ("page-down") ""
+                   ("page-up") "PgUp"
+                   ("page-down") "PgDn"
                    ("esc" "escape") "Esc"
                    ("backspace") "⌫"
                    ("delete") "Delete"