Make Electron build

I historically have never liked Electron, and I don't like it now, but
unfortunately due to poor browser support, I don't have a choice to
ship anything more lightweight if I want to use the Filesystem API
as part of the packaged build, which is kind of the point.

I guess it's true:
"You either die a hero or you live long enough to become the villain."

This is an experimental build.

electron/main.js

@@ -0,0 +1,76 @@
+const { app, BrowserWindow, shell } = require('electron');
+const http = require('http');
+const fs = require('fs');
+const path = require('path');
+
+const DIST = path.join(__dirname, 'dist');
+
+const MIME = {
+    '.html': 'text/html',
+    '.css': 'text/css',
+    '.js': 'application/javascript',
+    '.json': 'application/json',
+    '.wasm': 'application/wasm',
+    '.zip': 'application/zip',
+    '.tgz': 'application/gzip',
+    '.svg': 'image/svg+xml',
+    '.png': 'image/png',
+    '.ico': 'image/x-icon',
+    '.webmanifest': 'application/manifest+json',
+};
+
+let server;
+let win;
+
+function createWindow() {
+    win = new BrowserWindow({
+        width: 1200,
+        height: 900,
+        icon: path.join(DIST, 'favicon', 'favicon-96x96.png'),
+        autoHideMenuBar: true,
+        webPreferences: { contextIsolation: true },
+    });
+    const localOrigin = `http://localhost:${server.address().port}`;
+
+    win.loadURL(localOrigin);
+    win.on('closed', () => { win = null; });
+
+    const isExternal = (url) => {
+        try { return new URL(url).origin !== localOrigin; } catch { return false; }
+    };
+
+    win.webContents.on('will-navigate', (e, url) => {
+        if (isExternal(url)) { e.preventDefault(); shell.openExternal(url); }
+    });
+    win.webContents.setWindowOpenHandler(({ url }) => {
+        if (isExternal(url)) shell.openExternal(url);
+        return { action: 'deny' };
+    });
+}
+
+server = http.createServer((req, res) => {
+    const url = new URL(req.url, 'http://localhost');
+    let filePath = path.join(DIST, decodeURIComponent(url.pathname));
+
+    try {
+        const stat = fs.statSync(filePath);
+        if (stat.isDirectory()) filePath = path.join(filePath, 'index.html');
+    } catch {}
+
+    try {
+        fs.statSync(filePath);
+        res.writeHead(200, { 'Content-Type': MIME[path.extname(filePath)] || 'application/octet-stream' });
+        fs.createReadStream(filePath).pipe(res);
+    } catch {
+        res.writeHead(404, { 'Content-Type': 'text/plain' });
+        res.end('Not found');
+    }
+});
+
+server.listen(0, '127.0.0.1', () => {
+    app.whenReady().then(createWindow);
+});
+
+app.on('window-all-closed', () => { app.quit(); });
+
+app.on('before-quit', () => { server.close(); });