Add pagination blocks, renderCore, layout audit and react-pdf quirk tests

TableGuard, BottomSpacer, FirstPageHeader and PageChrome implement the
verified pagination rules; renderCore returns bytes, a normalised layout
tree, audit issues and a layout fingerprint. auditLayout detects overlaps,
ink overflow, truncation, header-only pages and split blocks. Quirk tests
pin the react-pdf behaviours the design depends on, and a child-process
test pins the page-level absolute Svg hang.

src/pdf/blocks/BottomSpacer.tsx

@@ -0,0 +1,13 @@
+import { View } from "@react-pdf/renderer";
+import { FILL } from "../engine/columns";
+import { pdfFlags } from "./pdfProps";
+
+/**
+ * Elastic gap before the closing block (amount in words, bank, signatory). It grows to push the closing
+ * block to the foot of whichever page it ends on. `closingH` is the closing block's height: as
+ * minPresenceAhead it keeps the spacer from staying on the previous page while the block starts the
+ * next one (without it the spacer stays behind and the block sits at the top of the new page).
+ */
+export function BottomSpacer({ closingH }: { closingH: number }) {
+  return <View style={FILL} {...pdfFlags({ minPresenceAhead: closingH })} />;
+}