Triage: test coverage baseline + CI gate

[ComfyChloe]

Part of the ARC-OSC workboard triage track.

What's needed

Decide the first testing baseline for the Electron client: which layers get automated tests first, what runner, and what CI gate makes regressions visible.

Scope

• Pick test runner and layout (unit vs integration vs e2e priority)
• Decide the minimum CI gate (lint + type-check + the chosen test layer)
• Define what counts as blocking vs advisory failures

Acceptance criteria

• Written triage decision for runner, layout, and CI gate
• Follow-up implementation issue(s) created from the decision

Out of scope: writing the tests themselves (separate issue after triage).