Fix Electron plotting: expose Plotly as a global

Electron wraps every renderer <script> in its own CommonJS module scope,
so const Plotly = require('plotly.js-dist') stayed module-local and the
bare Plotly references in myplots.js (Plot_xy) and TrimSPlib.js
(Plotly.purge) threw ReferenceError, breaking both the Plot menu popups
and the in-app Plots tab. Export window.Plotly = Plotly, matching the
window.openElectronAuxiliaryWindow pattern already used in the file.

TrimSPelec.js

@@ -2,6 +2,11 @@
 
 // Load required packages
 const Plotly = require('plotly.js-dist');
+// Electron wraps every renderer <script> in its own CommonJS module scope, so
+// the bundled Plotly object must be exported to the global scope explicitly.
+// myplots.js and TrimSPlib.js call Plotly.plot/relayout/purge as a global on
+// the main window and inside the Plot-menu popup windows.
+window.Plotly = Plotly;
 const ipcRenderer = require('electron').ipcRenderer;
 const fs = require('fs');
 const { execSync, execFile } = require('child_process');