Procurement: keep Documents' agreement/quote available post-acceptance

The Documents modal gated the agreement + quote on isIssued (quote status
sent/open), which flips false once the quote is accepted — so after signing
they wrongly read 'available once your quote is issued'. Gate on the quote's
stripeQuoteId instead, which is set at issuance and persists through
acceptance, so the reference stays available throughout the journey.

frontend/editor/src/portal/components/procurement/ProcurementFlow.tsx

@@ -209,7 +209,7 @@ export function ProcurementFlow({
           setEditing(false);
           setOpen(true);
         }}
-        quoteAvailable={isIssued}
+        quoteAvailable={!!latest?.stripeQuoteId}
         downloadingQuote={downloading}
         onDownloadQuote={onDownloadPdf}
         invoiceUrl={latest?.invoiceUrl}