Unify the provider-guard "throws outside its provider" test pattern

[Zaldaryon]

Two renderer tests assert that a context hook throws when used outside its provider, and they do it two different ways:

• tests/renderer-dom/configContextSlices.test.tsx:167 lets the render throw escape and silences the fallout: vi.spyOn(console, "error").mockImplementation(() => {}) plus a window error listener that calls preventDefault().
• tests/renderer-dom/taskManagerFlows.test.tsx (after test(renderer): keep the TaskProvider guard throw inside the component #264) catches the throw inside the render callback so React never runs its guarded replay, then asserts console.error was not called as a regression pin.

The catch-inside approach from #264 is the better one. It does not depend on jsdom's window error machinery or on Vitest's global error-listener bookkeeping, and it fails loudly if a future edit lets the throw escape again. #264 explains why the escaping form is a run-level flake risk.

Proposed, test-only, no production change:

1. Move configContextSlices.test.tsx:167 to the same catch-inside pattern.
2. useNotificationsContext (src/renderer/src/contexts/NotificationsContext.tsx:145) has no outside-provider test at all. Add one in the same style so that guard branch is covered.