feat(email-renderer): add global brand styling

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

@@ -63,6 +63,7 @@ describe("email renderer", () => {
     if (!first.ok) return;
     const value: EmailRenderBundle = first.value;
     expect(value.parts.html.content).toContain("Hello <world>");
+    expect(value.parts.html.content).toContain("color:#111827");
     expect(value.parts.text.content).toContain("Hello <world>");
     expect(value.parts.amp?.validation.valid).toBe(true);
     expect(value.exports?.mjml).toContain("<mjml>");