feat(shared): add getPretextFontString formatter

src/shared/lib/utils/getPretextFontString/getPretextFontString.ts

@@ -0,0 +1,16 @@
+/**
+ * Formats a font config into the string `@chenglou/pretext` and the Canvas 2D
+ * `font` property both expect: `weight sizepx "family"`.
+ *
+ * ponytail: deliberate copy of widgets/ComparisonView/lib's version — ADR-0002
+ * keeps the shelved morph tool untouched, so we don't move its util. Three lines
+ * is cheaper to duplicate than to refactor frozen code.
+ *
+ * @param weight - Numeric font weight (e.g. 400).
+ * @param sizePx - Font size in pixels.
+ * @param fontName - The font family name.
+ * @returns A formatted font string: `weight sizepx "fontName"`.
+ */
+export function getPretextFontString(weight: number, sizePx: number, fontName: string): string {
+    return `${weight} ${sizePx}px "${fontName}"`;
+}