fix(xref): follow-ups to the xref attach parity merge

- `XREF <args>` runs whole: probing the bare verb first now opens the
  External References palette, which refreshed every entry and toggled
  the palette before `XREF Reload A` / `XREF ?` ran.
- Update the two tests that encoded the old behaviour: `-XREF ?` prints
  the reference table, and attaching a missing file is rejected.
- Drop the duplicate "Specify On-screen" catalog entry that shadowed the
  translated common key, with its unused ftl keys.
- Move `remove_pipe_symbols`' doc comment back above its function.
- Note in `document_for_save` that resolved xref content stays out.
- Gate the desktop-only preview cap and tab index for wasm.

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

src/app/commands/xref_attach.rs

@@ -175,6 +175,7 @@ impl OpenCADStudio {
         path: &str,
     ) -> (Vec<crate::scene::model::wire_model::WireModel>, i16) {
         // ponytail: a huge reference skips the ghost; cap by entity count.
+        #[cfg(not(target_arch = "wasm32"))]
         const MAX_PREVIEW_ENTITIES: usize = 20_000;
         let scene = &self.tabs[i].scene;
         if let Some(name) = existing {
@@ -264,6 +265,7 @@ impl OpenCADStudio {
     /// Fills the dialog from the chosen file: name, preview, block unit and
     /// the paths shown under Details.
     fn load_xref_attach_file(&self, state: &mut XrefAttachState, path: &str) {
+        #[cfg(not(target_arch = "wasm32"))]
         let i = self.active_tab;
         state.path = path.to_string();
         state.name = path_to_block_name(path);