fix(quotes): guard possibly-undefined itemAt in isQuotePdfStale

Deployment was failing at `npm run build` with:
  quote-pdf-service.ts(487,10): error TS18048: 'itemAt' is possibly 'undefined'

`itemAt` comes from `latestItem.items[0]?.updated` (row type
`{ updated?: string }`), so it's `string | undefined`, while `pdfAt`
was already narrowed to `string` by the earlier `if (!pdfAt)` guard —
comparing the two fails under strict mode.

Semantically, a quote with no active items left (all moved/removed)
has no item timestamp, and that alone shouldn't mark the PDF stale;
only the quote-level timestamp decides in that case.

Verified with a full `npm run build` (exit 0).

src/lib/server/quote-pdf-service.ts

@@ -484,5 +484,9 @@ export async function isQuotePdfStale(quoteId: string): Promise<boolean> {
   // matches chronological compare for ISO 8601 with consistent
   // timezone offsets, which PB always emits (UTC, no fractional
   // seconds). `String(a) > String(b)` is sufficient.
-  return itemAt > pdfAt || quoteAt > pdfAt;
+  //
+  // `itemAt` is undefined when the quote has no active items left
+  // (all moved/removed) — that alone doesn't make the PDF stale, so
+  // only the quote-level timestamp decides in that case.
+  return (itemAt !== undefined && itemAt > pdfAt) || quoteAt > pdfAt;
 }