fix(email-renderer): honor explicit heading typography

packages/email-renderer/test/heading-size.test.ts

@@ -0,0 +1,13 @@
+import { expect, test } from "bun:test";
+import { renderEmail } from "../src/index.ts";
+
+test("explicit heading sizes are not multiplied by browser heading defaults", async () => {
+  for (const size of [undefined, "36px", "expression(1)"]) {
+    const result = await renderEmail({schemaVersion:1,kind:"email",meta:{subject:"Typography",lang:"en"},theme:{tokens:{}},root:{id:"root",type:"layout.email-document",version:1,props:{width:"600"},styles:{},slots:{content:[{id:"heading",type:"content.heading",version:1,props:{text:"Design that works",level:"1"},styles:size?{fontSize:{base:size}}:{},slots:{}}]}}}, {amp:false,mjml:false});
+    expect(result.ok).toBe(true);
+    if (!result.ok) continue;
+    const html=result.value.parts.html.content;
+    expect(html.includes("font-size:inherit;line-height:1.2;")).toBe(size === "36px");
+    expect(html).not.toContain("expression(");
+  }
+});