feat(11-receipt-print): phase 11 complete — receipt preview, print & PDF

Add receipt show/print/pdf endpoints with dompdf integration.
Active preview and PDF links in order Documents tab.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.vscode/ftp-kr.json

@@ -17,7 +17,7 @@
     ".gitignore",
     "/.scannerwork",
     "/.paul",
-    "/vendor",
+    "/vendor/bin",
     "/node_modules",
     "/composer.phar",
     "/composer.lock",