Install updates silently and relaunch

[enaboapps]

Summary

Downloaded updates currently call quitAndInstall(false, true), which can show the visible NSIS installer flow and leave users blocked at the finish step. Install updates silently and force relaunch after app-triggered update installation.

Scope

• Use silent install for downloaded updates.
• Keep forced relaunch after install.
• Update the install button label to make restart behavior clear.
• Make NSIS run-after-finish intent explicit.
• Update focused tests.

Acceptance criteria

• Downloaded updates call quitAndInstall(true, true).
• The update install button says Install and restart.
• NSIS config explicitly keeps runAfterFinish: true.
• npm test -- src/main/updates/update-service.test.ts passes.
• npm test passes.
• npm run build passes.