Selection tools on the right-edge toolbar instead of contextual tabs

The PDF Underlay and External Reference ribbon tabs are gone. While only
PDF underlays are selected their tools (Display in Monochrome, Create
Clipping Boundary, Remove Clipping, Show Underlay, Enable Snap, External
References, Edit Layers, Import As Objects) sit on the right-edge toolbar,
the switches drawn as on while on; while only xrefs are selected the xref
tools do. Contrast and fade stay in Properties. Toolbar tooltips are
translated.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/ui/ribbon/widgets.rs

@@ -40,9 +40,6 @@ pub(super) struct ToggleState {
     pub show_block_palette: bool,
     pub show_file_tabs: bool,
     pub show_layout_tabs: bool,
-    pub underlay_mono: bool,
-    pub underlay_shown: bool,
-    pub underlay_snap: bool,
 }
 
 // ── Layout constants (single source of truth: ROW_H from ui::mod) ─────────
@@ -378,9 +375,6 @@ pub(super) fn is_active_tool(
         "UCSICON" => state.show_ucs_icon,
         "PROPERTIES" => state.show_properties,
         "BLOCKPALETTE" => state.show_block_palette,
-        "_PDFULMONO" => state.underlay_mono,
-        "_PDFULSHOW" => state.underlay_shown,
-        "_PDFULSNAP" => state.underlay_snap,
         "FILETAB" => state.show_file_tabs,
         "LAYOUTTAB" => state.show_layout_tabs,
         id => active_tool.as_deref() == Some(id),