feat(electron): walking skeleton for the desktop shell

Phase 1 step 1 of VNCprodbuild: electron/main.ts boots the same Next.js
"standalone" server artifact the Dockerfile already produces (next.config.ts's
output: "standalone") as a child process on a random localhost port, then
opens a BrowserWindow at it. electron/preload.ts is a contextBridge stub
(window.vnc.isElectron) for now.

scripts/assemble-standalone.mjs copies public/ and .next/static into
.next/standalone, mirroring what the Dockerfile does by hand, since `next
build` deliberately leaves both out of the standalone output.
scripts/build-electron.mjs bundles main.ts/preload.ts to CommonJS via esbuild
(already a devDependency).

New npm scripts: build:standalone, build:electron, electron:dev.
electron-builder.config.js is intentionally minimal - no signing, no
platform targets yet, just enough to prove the concept end to end.

Also fixes a pre-existing repo-wide lint gap: vnc/plugins/smime is an
independent sub-package (own package.json/esbuild build, browser-only
globals) that was never added to eslint's ignores alongside repos:: and
examples/**, so `npm run lint` - and the husky pre-commit hook - was failing
on every commit regardless of what changed. Excluded it the same way those
are, and added node globals for scripts/**/*.mjs so the new build helpers
above lint cleanly too.

Verified manually: npm run build:standalone && npm run build:electron &&
electron . boots the server and opens a window with no errors.

scripts/assemble-standalone.mjs

@@ -0,0 +1,29 @@
+#!/usr/bin/env node
+// `next build --webpack` (see next.config.ts's `output: "standalone"`)
+// emits .next/standalone/server.js but - deliberately, per Next's own docs -
+// leaves out public/ and .next/static/. The Dockerfile copies both in by
+// hand for the container image; this does the same thing for local Electron
+// dev and packaging, so every path boots the exact same artifact.
+import { cpSync, existsSync, rmSync } from "node:fs";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+
+const rootDir = path.dirname(path.dirname(fileURLToPath(import.meta.url)));
+const standaloneDir = path.join(rootDir, ".next", "standalone");
+
+if (!existsSync(standaloneDir)) {
+  console.error(`Missing ${standaloneDir} - run "next build --webpack" first.`);
+  process.exit(1);
+}
+
+const publicSrc = path.join(rootDir, "public");
+const publicDest = path.join(standaloneDir, "public");
+rmSync(publicDest, { recursive: true, force: true });
+cpSync(publicSrc, publicDest, { recursive: true });
+
+const staticSrc = path.join(rootDir, ".next", "static");
+const staticDest = path.join(standaloneDir, ".next", "static");
+rmSync(staticDest, { recursive: true, force: true });
+cpSync(staticSrc, staticDest, { recursive: true });
+
+console.log("Assembled standalone server at", standaloneDir);