Function configureSignal

Configure the signal factory. Called once by chamber.ts after its async Vue probe completes; also available to consumers who want a custom signal implementation.

Dev note: if any signals were created BEFORE this call resolved a reactive backing, those signals are plain { value } objects forever — writes to them will not trigger Vue reactivity, while signals created after this call will. A one-shot dev warning fires in that case; to guarantee a uniform backing, await waitForVueDetection() before the first signal() call.