feat(invoice): make the phone number on the PDF a clickable tel: link

Wraps the phone in a @react-pdf 'Link' with src='tel:+\u2026' just like the
existing email (mailto:) and website (https:) entries in the contact
footer. Display string keeps the human-readable formatting (spaces,
parens) while the underlying URL is normalized per RFC 3966 (digits
plus an optional leading '+').

PDF readers on macOS, iOS, Android and most desktop Linux setups
launch the system dialer or a VoIP app on click; readers without a
'tel' handler fall back to selecting the number.

app/services/invoice/pdf/InvoiceDocument.tsx

@@ -588,7 +588,11 @@ function Footer({ issuer, language }: { issuer: IssuerData; language: InvoiceLan
       </View>
       <View style={styles.footerCol}>
         <Text style={styles.footerHeading}>{t.contactHeading}</Text>
-        {issuer.phone ? <Text>{t.phoneLabel}: {issuer.phone}</Text> : null}
+        {issuer.phone ? (
+          <Text>
+            {t.phoneLabel}: <Link src={toTelUrl(issuer.phone)}>{issuer.phone}</Link>
+          </Text>
+        ) : null}
         {issuer.email ? (
           <Text>
             {t.emailLabel}: <Link src={`mailto:${issuer.email}`}>{issuer.email}</Link>
@@ -644,6 +648,21 @@ function normaliseWebUrl(url: string): string {
   return `https://${trimmed.replace(/^\/\//, "")}`;
 }
 
+/**
+ * Build a `tel:` URL from a free-form phone string. RFC 3966 allows only
+ * digits and a leading `+`, so we strip everything else (spaces, parens,
+ * dashes, slashes, dots, internal letters). The display string above the
+ * link keeps the human-readable formatting.
+ */
+function toTelUrl(phone: string): string {
+  const cleaned = phone.replace(/[^\d+]/g, "");
+  // Keep only a single leading '+' if present.
+  const normalized = cleaned.startsWith("+")
+    ? "+" + cleaned.slice(1).replace(/\+/g, "")
+    : cleaned.replace(/\+/g, "");
+  return `tel:${normalized}`;
+}
+
 /**
  * Turn a Shopify payment-gateway machine name (e.g. `shopify_payments`,
  * `manual`, `bogus`) or a built-in manual-payment template name (e.g.