Insert Reference panel: separate Attach XREF and Attach PDF buttons

The single Attach button gives way to Attach XREF (XATTACH, the external
reference picker and dialog) and Attach PDF (PDFATTACH, the PDF picker and
Attach PDF Underlay dialog) with their own icons. ATTACH stays available
as a command. The Turkish label reads "PDF Bağla".

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

src/modules/insert/mod.rs

@@ -52,6 +52,7 @@ impl CadModule for InsertModule {
                     title: "Reference",
                     tools: vec![
                         RibbonItem::LargeTool(xattach::tool()),
+                        RibbonItem::LargeTool(pdf_attach::tool()),
                         RibbonItem::LargeTool(xclip::tool()),
                         RibbonItem::LargeTool(xadjust::tool()),
                         RibbonItem::LabeledTool(underlay_layers::tool()),