Xref attach: Attach dialog, reference prompts, and xref drawings other applications can open

Attach External Reference dialog after XATTACH / ATTACH; ATTACH routes
drawings, PDFs and images; placement prompts and messages follow the
reference (presets, Corner/XYZ, nonzero check, existing definition reuse,
missing file, self-reference); name keeps the file's case; overlay and
path type at attach; one undo step for definition and INSERT; -XREF option
prompt and `?` table; XREF opens the palette; ER alias; xref Properties
rows; dependent symbols flagged and remapped and resolved content left out
of the saved file; dialog_ok automation action; localized labels.

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

src/app/view/modal.rs

@@ -24,6 +24,7 @@ impl OpenCADStudio {
             Some(K::LayerTranslator) => crate::t!("Layer Translator").into_owned(),
             Some(K::DrawingUnits) => crate::t!("Drawing Units").into_owned(),
             Some(K::BlockDefinition) => crate::t!("Block Definition").into_owned(),
+            Some(K::XrefAttach) => crate::t!("Attach External Reference").into_owned(),
             Some(K::GeometricTolerance) => crate::t!("Geometric Tolerance").into_owned(),
             Some(K::DraftingSettings) => crate::t!("Drafting Settings").into_owned(),
             Some(K::AutoConstrainSettings) => crate::t!("Constraint Settings").into_owned(),
@@ -506,6 +507,13 @@ impl OpenCADStudio {
                     crate::ui::window::block_definition::view_window(state, flow)
                 })
             }
+            super::super::ModalKind::XrefAttach => {
+                let state = self.xref_attach.as_ref()?;
+                let height = if state.details { 520 } else { 450 };
+                sized_flow(ex, 740, height, |flow| {
+                    crate::ui::window::xref_attach::view_window(state, flow)
+                })
+            }
             super::super::ModalKind::GeometricTolerance => {
                 let state = self.geometric_tolerance.as_ref()?;
                 sized_flow(ex, 670, 530, |flow| {