fix(documents): SigningDetailsDialog — partially_signed key match

mapWorkflowStatus had key 'partial:' but the schema status string is
'partially_signed'. The mismatch fell through to the 'pending' default
so a partially-signed workflow rendered the wrong pill colour. Aligns
the lookup key with the actual status enum.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/documents/signing-details-dialog.tsx

@@ -150,7 +150,7 @@ function mapWorkflowStatus(status: string): StatusPillStatus {
     pending: 'pending',
     draft: 'draft',
     sent: 'sent',
-    partial: 'partial',
+    partially_signed: 'partial',
     completed: 'completed',
     signed: 'signed',
     expired: 'expired',