Add typography roles, text primitives, fontkit measurer and layout lint

Txt always sets an absolute line height; RenderTxt never does. Row pins
every cell and stacks when the fill column would be too narrow. IdText and
FitText shrink then chunk or truncate. The fontkit measurer matches react-pdf
text widths exactly. A TypeScript-AST lint test enforces the layout rules
(no lineHeight outside Txt, no non-literal fixed/wrap/minPresenceAhead,
flexGrow needs flexBasis, no stray absolute positioning).

src/pdf/blocks/RenderTxt.tsx

@@ -0,0 +1,33 @@
+import { Text } from "@react-pdf/renderer";
+import { FILL, pinned } from "../engine/columns";
+import { roleToken, type RoleName, type TypeToken } from "../fonts/roles";
+import { pdfFlags, type PdfFlagsInput } from "./pdfProps";
+import { assertNoLineHeight, baseTextStyle, type TxtStyleProps } from "./Txt";
+
+export interface RenderTxtProps extends TxtStyleProps, PdfFlagsInput {
+  /** Receives { pageNumber, totalPages, subPageNumber, ... } from react-pdf. */
+  render: (info: { pageNumber: number; totalPages: number; subPageNumber: number; subPageTotalPages: number }) => string;
+  role: RoleName | TypeToken;
+  width?: number;
+  grow?: boolean;
+  style?: Record<string, unknown>;
+}
+
+/**
+ * Text drawn from a render prop (page numbers, continuation band). It sets NO lineHeight, and no
+ * ancestor may set one either: react-pdf multiplies a render-prop lineHeight again on every relayout
+ * ('10pt' ends up as 5120 and nothing draws). The box is auto-height; reserve its space from font
+ * metrics, never a fixed height. No maxLines: a clamped render-prop Text draws nothing.
+ * `totalPages` is undefined on the first layout pass, so the render function must cope with that.
+ */
+export function RenderTxt({ role, render, color, align, weight, italic, width, grow, style, faceOverrides, fixed, wrap, minPresenceAhead }: RenderTxtProps) {
+  const token = roleToken(role);
+  assertNoLineHeight(style, "RenderTxt");
+  const merged = {
+    ...baseTextStyle(token, { color, align, weight, italic, faceOverrides }),
+    ...(width !== undefined ? pinned(width) : {}),
+    ...(grow ? FILL : {}),
+    ...style,
+  };
+  return <Text style={merged as never} render={render as never} {...pdfFlags({ fixed, wrap, minPresenceAhead })} />;
+}