Add a core script engine; wire File ▸ Run script in the wx GUI.

The wx frontend had no way to run essim command scripts (only the tui shell
did). Add a frontend-agnostic engine in core/app/script.{hpp,cpp}:
run_script(unique_ptr<System>&, path, ostream&) -> {ok, error, lines, errors}.
It parses essim scripts (# comments, blank lines, "quoted" args, set + $var /
${var} expansion, nested source with a depth guard) and dispatches the
scriptable, system-building commands — new, load, connect, set-connector-type,
set-signal-type, attach-bsdl, verify, export, save, restore — to the existing
app::* operations, writing their (TUI-identical) output to the stream.
Unsupported/interactive commands are reported and counted, execution continues.
System is taken by reference so new/restore can replace it.

wx gains File ▸ Run script…: pick a .essim, run it, echo the output into the
log and refresh. WxFrontend exposes system_ptr() for the engine.

tests/test_script.cpp: a full script (comment + set/$var + new + load + set-
signal-type + verify) builds the system and produces the expected log; missing
file reported; unsupported command flagged and skipped. 400 core assertions
green; tui + wx build clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/frontends/wx/wx_frame.cpp

@@ -6,6 +6,7 @@
 #include "core/app/edit.hpp"
 #include "core/app/export.hpp"
 #include "core/app/load.hpp"
+#include "core/app/script.hpp"
 #include "core/app/verify.hpp"
 #include "core/domain/analysis.hpp"
 #include "core/domain/connect.hpp"
@@ -26,6 +27,7 @@
 
 #include <algorithm>
 #include <cctype>
+#include <sstream>
 #include <string>
 #include <vector>
 
@@ -33,6 +35,7 @@ namespace {
 enum {
     ID_LOAD = wxID_HIGHEST + 1,
     ID_RESTORE,
+    ID_RUN_SCRIPT,
     ID_SAVE,
     ID_EXPORT,
     ID_SET_CONNECTOR_TYPE,
@@ -116,6 +119,7 @@ EssimFrame::EssimFrame(WxFrontend &fe)
     auto *file = new wxMenu;
     file->Append(ID_LOAD,    "&Load module…\tCtrl-L");
     file->Append(ID_RESTORE, "&Restore snapshot…\tCtrl-R");
+    file->Append(ID_RUN_SCRIPT, "&Run script…\tCtrl-U");
     file->Append(ID_SAVE,    "&Save snapshot…\tCtrl-S");
     file->AppendSeparator();
     file->Append(ID_EXPORT,  "&Export connections…\tCtrl-E");
@@ -169,6 +173,7 @@ EssimFrame::EssimFrame(WxFrontend &fe)
     Bind(wxEVT_MENU, &EssimFrame::OnLoad,    this, ID_LOAD);
     Bind(wxEVT_MENU, &EssimFrame::OnRestore, this, ID_RESTORE);
     Bind(wxEVT_MENU, &EssimFrame::OnSave,    this, ID_SAVE);
+    Bind(wxEVT_MENU, &EssimFrame::OnRunScript, this, ID_RUN_SCRIPT);
     Bind(wxEVT_MENU, &EssimFrame::OnExport,  this, ID_EXPORT);
     Bind(wxEVT_MENU, &EssimFrame::OnSetConnectorType, this, ID_SET_CONNECTOR_TYPE);
     Bind(wxEVT_MENU, &EssimFrame::OnAttachBsdl, this, ID_ATTACH_BSDL);
@@ -350,6 +355,32 @@ void EssimFrame::OnRestore(wxCommandEvent &) {
     RebuildModelView();
 }
 
+void EssimFrame::OnRunScript(wxCommandEvent &) {
+    wxFileDialog dlg(this, "Run an essim script", "", "",
+                     "essim scripts (*.essim)|*.essim|All files (*.*)|*.*",
+                     wxFD_OPEN | wxFD_FILE_MUST_EXIST);
+    if (dlg.ShowModal() != wxID_OK) return;
+
+    fe_.ensure_system();
+    std::ostringstream out;
+    app::ScriptResult r =
+        app::run_script(fe_.system_ptr(), dlg.GetPath().utf8_string(), out);
+
+    if (!r.ok) {
+        Log("run script: " + wx(r.error));
+        wxMessageBox(wx(r.error), "Run script", wxOK | wxICON_ERROR, this);
+        return;
+    }
+
+    // Echo each line of the script's output into the log pane.
+    std::istringstream lines(out.str());
+    std::string line;
+    while (std::getline(lines, line)) Log(wx(line));
+    Log(wxString::Format("source: %s  (%d line(s), %d error(s))",
+                         dlg.GetPath(), r.lines, r.errors));
+    RebuildModelView();
+}
+
 void EssimFrame::OnSave(wxCommandEvent &) {
     wxFileDialog dlg(this, "Save system snapshot", "", "system.essim",
                      "essim snapshots (*.essim)|*.essim|All files (*.*)|*.*",