Add installment calculator and Latin digits in English product text.

Wire the product CTA to store-loan-methods calculate so shoppers can pick a term and see the plan, and render English model runs under Montserrat so fanum fonts stop painting 0-9 as Persian digits.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/lib/mixedText.ts

@@ -0,0 +1,44 @@
+// IRANYekan *fanum* maps Latin digit codepoints (0-9) to Persian glyphs.
+// Montserrat (`.en`) keeps real Latin digits — so any Latin-letter run that
+// also carries model numbers (HP R5, 8GB, EF2126WM…) must render under `.en`.
+// Pure digit runs (e.g. "13" inside «آیفون 13 پرو») stay on the FA font and
+// correctly show as Persian digits.
+const EN_RUN = /[A-Za-z0-9][A-Za-z0-9\s\-_|./+#%]*/g;
+
+export type TextSegment = { type: "fa" | "en"; text: string };
+
+export function splitMixedText(text: string): TextSegment[] {
+  const segments: TextSegment[] = [];
+  let cursor = 0;
+  let match: RegExpExecArray | null;
+  const re = new RegExp(EN_RUN.source, "g");
+
+  while ((match = re.exec(text)) !== null) {
+    let start = match.index;
+    let end = start + match[0].length;
+    while (end > start && /\s/.test(text[end - 1]!)) end--;
+    const chunk = text.slice(start, end);
+    if (!/[A-Za-z]/.test(chunk)) continue;
+
+    if (start > cursor) segments.push({ type: "fa", text: text.slice(cursor, start) });
+    segments.push({ type: "en", text: chunk });
+    cursor = end;
+  }
+
+  if (cursor < text.length) segments.push({ type: "fa", text: text.slice(cursor) });
+  return segments;
+}
+
+/** Wrap Latin runs in a plain string as `.en` spans (text is assumed already HTML-safe). */
+export function wrapLatinRuns(text: string): string {
+  return splitMixedText(text)
+    .map((seg) =>
+      seg.type === "en" ? `<span class="en" dir="ltr" lang="en">${seg.text}</span>` : seg.text,
+    )
+    .join("");
+}
+
+/** Walk HTML text nodes (content between tags) and wrap Latin runs. */
+export function wrapLatinInHtml(html: string): string {
+  return html.replace(/(^|>)([^<]+)/g, (_, prefix: string, text: string) => prefix + wrapLatinRuns(text));
+}