feat(viewer): add PrintMode for browser print/PDF export

Adds RenderOptions.PrintMode flag. When true:
- view.js (table filters) is not loaded
- window.print() fires on page load
- @media print CSS hides filters, collapses grid to single column,
  adds page-break hints for section cards

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

viewer/model.go

@@ -3,6 +3,7 @@ package viewer
 type pageData struct {
 	Title                string
 	HasSnapshot          bool
+	PrintMode            bool
 	Error                string
 	NoticeTitle          string
 	NoticeBody           string