Add the Northline template family: Purple Pop and Citrus Split

Purple Pop (cream page, purple pills, asterisk and dome decor, opt-in
logo) and Citrus Split (grey split panel, halftone chevrons, icon
contacts, logo in the measured slot) are rebuilt from the reference PDFs on
the engine with A4/Letter support, GST slots and zero audit errors. Adds
static DM Sans, Jost and Poppins 800 as look-alikes for the commercial
fonts. The picker now lists ten templates.

src/pdf/decor/Underlay.tsx

@@ -0,0 +1,21 @@
+import { View } from "@react-pdf/renderer";
+import { pdfFlags } from "../blocks/pdfProps";
+import type { DecorItem } from "../blocks/FirstPageHeader";
+import { DECOR_ID } from "../engine/ids";
+
+/**
+ * Fixed, page-anchored boxes painted BEFORE the flow, so the text of the flow sits on top of them: a panel the
+ * numbers are printed on, watermarks, halftone dots. PageChrome's decor is painted after the flow and would
+ * cover it. Render this as the first child of the Page.
+ */
+export function Underlay({ items }: { items: DecorItem[] }) {
+  return (
+    <>
+      {items.map((d, i) => (
+        <View key={i} id={DECOR_ID} style={{ position: "absolute", left: d.x, top: d.y, width: d.width, height: d.height }} {...pdfFlags({ fixed: true })}>
+          {d.children}
+        </View>
+      ))}
+    </>
+  );
+}