feat(md-print): use mm font and corner page numbers

Body font size is now specified in millimetres and defaults to 3mm. Page numbers move from the centre footer to the outer bottom corners, alternating left and right per A5 page.

src/components/md-print/paginate.ts

@@ -54,7 +54,7 @@ export function createPageElement(opts: PaginateOptions): {
   page.style.position = "relative";
   page.style.overflow = "hidden";
   page.style.background = "white";
-  page.style.setProperty("--md-print-font-size", `${opts.font}pt`);
+  page.style.setProperty("--md-print-font-size", `${opts.font}mm`);
 
   if (opts.title) {
     const header = document.createElement("div");