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/package.json

@@ -18,7 +18,9 @@
     "build:electron": "pnpm build && electron-builder",
     "preview": "vite preview",
     "typecheck": "vue-tsc --noEmit",
-    "lint": "eslint src/"
+    "lint": "eslint src/",
+    "test": "vitest run",
+    "test:watch": "vitest"
   },
   "dependencies": {
     "@bitSpire/clink": "workspace:*",
@@ -55,6 +57,7 @@
     "tw-animate-css": "^1.4.0",
     "typescript": "^5.7.0",
     "vite": "^6.0.0",
+    "vitest": "^2.1.9",
     "vue-tsc": "^2.1.0"
   },
   "build": {