Surface Save as PDF via existing print flow (#587)

Rename the Options menu item from "Print Plan" to "Print / Save as PDF"
with a subtitle guiding users to pick "Save as PDF" as the print
destination. Linked docs, plan diff, annotate mode, and archive mode
all render through the same Viewer's [data-print-region="article"],
so print.css already covers them with no further changes.

Author: backnotprop

packages/ui/components/PlanHeaderMenu.tsx

@@ -151,7 +151,8 @@ export const PlanHeaderMenu: React.FC<PlanHeaderMenuProps> = ({
               onPrint();
             }}
             icon={<PrintIcon />}
-            label="Print Plan"
+            label="Print / Save as PDF"
+            subtitle="Choose 'Save as PDF' in the print dialog"
           />
           {sharingEnabled && (
             <ActionMenuItem