fix : dont break new line on export image

lib/guides/image-export.test.tsx

@@ -5,6 +5,7 @@ import { describe, expect, it } from "vitest";
 import {
   GuideImageExport,
   imageExportFileName,
+  scaledExportFontSize,
 } from "@/components/public/guide-image-export";
 import { MaterialPoster } from "@/components/public/material-poster";
 import { ConstellationImage } from "@/components/public/constellation-image";
@@ -104,6 +105,20 @@ describe("image export filenames", () => {
   });
 });
 
+describe("image export text fitting", () => {
+  it("keeps the original font size when text already fits", () => {
+    expect(scaledExportFontSize(32, 180, 240)).toBe(32);
+  });
+
+  it("scales overflowing text to the available width", () => {
+    expect(scaledExportFontSize(32, 320, 240)).toBe(24);
+  });
+
+  it("has no minimum font-size floor for exceptionally long text", () => {
+    expect(scaledExportFontSize(32, 3200, 100)).toBe(1);
+  });
+});
+
 
 describe("material poster text", () => {
   const props = {