test(desktop): install the Electron binary once before the unit suite

Electron 44 downloads its binary on the first Node require("electron")
instead of at npm ci. Vitest workers importing electron-log/main raced
that download and extraction (File exists on dist/electron, then
"Electron failed to install correctly" in a sibling worker) on both
Ubuntu and Windows desktop-tests jobs. Run the package's idempotent
install-electron in one process before vitest forks.

packages/desktop/package.json

@@ -23,7 +23,7 @@
     "test:e2e:renderer": "cross-env E2E_DESKTOP_RUNTIME=1 playwright test --config=playwright.config.ts --project=desktop",
     "test:e2e:browser-tabs": "npm run build:main && node ./e2e/browser-tabs.e2e.mjs",
     "verify:electron-cdp": "node ./scripts/verify-electron-cdp.mjs",
-    "test": "vitest run --exclude \"e2e/**\"",
+    "test": "install-electron && vitest run --exclude \"e2e/**\"",
     "typecheck": "tsgo --noEmit -p tsconfig.json",
     "test:e2e:lifecycle": "npm run build:main && node ./e2e/daemon-lifecycle.e2e.mjs"
   },