ui: File › New starts an empty model (file.new, #144); an unknown sample name opens the samples (#200)

file.new replaces the session with an empty one: no design, mesh, definitions, results or
journal, nothing to save, the undo history empty. The File menu and Cmd/Ctrl+N run it, asking
first over unsaved changes. A sample name the app does not know (a typo, an old ?sample= link)
opens the samples to choose from, and the status names it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/ui-egui/src/control.rs

@@ -248,6 +248,7 @@ pub fn handle(app: &mut ModelApp, ctx: &egui::Context, req: &ControlRequest) ->
                     crate::files::Replace::File(p) => p.clone(),
                     crate::files::Replace::Sample(n) => format!("sample {n}"),
                     crate::files::Replace::Update => "update".to_string(),
+                    crate::files::Replace::New => "new".to_string(),
                 }}),
                 crate::files::Prompt::Recover => json!("recover"),
                 crate::files::Prompt::Samples => json!("samples"),