Print button is disabled while a job is being sent and a spinner shows
in the footer. On success a transient 'Sent to printer' confirmation is
displayed for a few seconds; on failure the error message stays in the
footer instead of replacing the document view.
- Remove menu bar from header_start (it consumed mouse wheel events)
- Add Print button in footer alongside page info
- Remove unused About message and menu code
- Scroll of mouse wheel now works correctly for page navigation
- Add Print command to DocumentCommand enum
- Add File menu bar with Print and About items
- Implement print_document_sync() using CUPS lp command
- Raster images converted to PDF via img2pdf (fallback: ImageMagick)
- SVG converted to PDF via pdftocairo → img2pdf
- PDF sent directly to printer via lp
- Ctrl+P keyboard shortcut (via ModifiersChanged subscription)
- Print status tracking with printing flag to prevent duplicates
- Rename SessionKind → CollectionKind
- Replace monolithic DocumentCommand with SessionCommand (lifecycle + collection)
and DocumentCommand (reserved for future document operations)
- Separate session creation from population (New → Select → AddDirectory)
- Collection commands operate on active session, no hidden side effects
- RemoveDocument/CopyDocument use explicit indices (no more Option)
