chore(machine): set up vitest for apps/machine

First test surface for the Electron + Vue 3 app — apps/machine has had
no tests until now (workspace packages cover state-machine, nostr-client,
clink, lnbits). Cassette config #56 shipped untested under the same
posture; #57 (operator fee config consumer) introduces enough load-
bearing parser + state-store logic to want unit coverage, so growing
the test substrate now.

Adds `test` / `test:watch` scripts + vitest devDep + minimal config
that picks up `src/**/*.test.ts` and `electron/**/*.test.ts`. No tests
land here — that comes with the feature commit.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/machine/vitest.config.ts

@@ -0,0 +1,15 @@
+import { defineConfig } from 'vitest/config'
+import { fileURLToPath, URL } from 'node:url'
+
+export default defineConfig({
+  resolve: {
+    alias: {
+      '@': fileURLToPath(new URL('./src', import.meta.url)),
+    },
+  },
+  test: {
+    include: ['src/**/*.test.ts', 'electron/**/*.test.ts'],
+    globals: false,
+    environment: 'node',
+  },
+})