test(gui): assert destructive menu items are marked at rest, not on hover

[fstubner]

The e2e suite failed on a run of the current app:

Exit icon should be neutral before hover
actual:   rgb(244, 117, 130)
expected: rgb(149, 157, 174)

The app is right; the assertion was stale. #296 moved the red to rest deliberately — a warning that arrives once you have already aimed at the item is too late to redirect you. That PR changed four source files and no e2e file, so assertExitMenuItemNeutralUntilHover kept encoding the behaviour it replaced. Renamed, since the old name asserted the old rule.

What the new assertion pins

• Exit's icon is danger-coloured at rest
• A non-destructive item is not
• Hover keeps the marking rather than introducing it — menu.css covers hover as "a subset" of at-rest, so a rule that reverted there would be a regression the at-rest check alone would miss

The expected colour is read from --red through a probe element rather than a hardcoded hex, so it holds in both themes (#f47582 dark, #c6293d light) and getComputedStyle normalises it to the same rgb() form the icon reports.

The probe goes inside .container. tokens.css declares the palette there, not on :root — a first attempt appended it to document.body, where var(--red) resolved to nothing and inherited white. rawRed is now asserted non-empty so that failure reports itself instead of surfacing as a confusing colour mismatch.

Verification

Ran the suite against the built app: exit 0, no assertion errors, and all 12 screenshots rewritten through to tauri-render-narrow.png, which is the last one the run produces. eslint clean.

Note the suite is silent on success — it prints only on failure, so a passing run's log is just the build output.