Feature Request: Add Full Dark Mode Support for Cypress Test Runner (including Edge/Electron window background)

[mkowalski9]

Our team uses Cypress heavily and is forecasting increased usage across multiple products. We often keep the Test Runner open for long periods while developing and debugging specs. The current runner UI uses a bright, non‑themeable background — including the Edge/Electron window area outside the runner panel — which creates significant eye strain in dark‑theme development environments.
This is especially noticeable when the runner is open for hours during active development. The bright white background contrasts sharply with modern IDEs, terminals, and browsers that all support dark mode. The result is a jarring visual experience that breaks focus and increases fatigue.
We are also eagerly waiting for Vite 8 support in Cypress (expected around April). Since Vite 8 brings major performance improvements and is a natural milestone for many teams upgrading their tooling, this could be an ideal time to introduce a dark mode option for the Test Runner.

Prosed config enhancement.
{
"runnerTheme": "dark" // default/system?
}