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/alias.rs

@@ -74,8 +74,8 @@ const WEB_ALIAS_KEY: &str = "opencadstudio.aliases";
 /// defaults add aliases or change a default target, so existing profiles can be
 /// migrated forward (see `introduced_at` / `migrate_aliases`). Version 1 shipped
 /// the pre-REDRAW table; version 2 introduced the REDRAW-family aliases; version 3
-/// introduced HB (HATCHTOBACK).
-const DEFAULT_ALIASES_VERSION: u32 = 3;
+/// introduced HB (HATCHTOBACK); version 4 introduced ER (EXTERNALREFERENCES).
+const DEFAULT_ALIASES_VERSION: u32 = 4;
 
 #[cfg(target_arch = "wasm32")]
 const WEB_ALIAS_VERSION_KEY: &str = "opencadstudio.aliases.version";
@@ -93,6 +93,7 @@ fn introduced_at(version: u32) -> &'static [(&'static str, &'static str)] {
             ("REA", "REGENALL"),
         ],
         3 => &[("HB", "HATCHTOBACK")],
+        4 => &[("ER", "EXTERNALREFERENCES")],
         _ => &[],
     }
 }