fix: wire orphaned IPC channels, fix data-loss bug, print preview events, sidebar navigation

- Fix file.clearRecent sending IPC to main process instead of clearing openTabs
- Wire show-batch-converter, show-document-compare, open-header-footer-dialog IPC channels
- Add print preview event listeners (mc:print-preview, mc:print-preview-styled) in App.tsx
- Fix sidebar hidden bridge buttons toggling sidebar closed after scroll
- Update sidebar menu labels to match actual sections (Files, Outline, Git)
- Fix ipc.print to be an object with show/doPrint methods (was bare function)
- Update callers: ExportPdfDialog, pdf-export, PrintPreview
- Add 7 regression tests for all fixes
- Clean 2 obsolete snapshots
- Build Linux packages (deb, AppImage, snap) — 549 tests passing

src/renderer/lib/pdf-export.ts

@@ -41,7 +41,7 @@ export async function generatePdf(options: PdfExportOptions): Promise<void> {
 
   // Hand the rendered HTML to the main process for native print-to-PDF.
   // This avoids the print dialog and works headlessly.
-  const result = await ipc.print({ html: finalHtml });
+  const result = await ipc.print.show({ html: finalHtml });
   if (!result.ok) {
     toast.error(`PDF export failed: ${result.error?.message ?? 'unknown error'}`);
   } else {