Add the framework-independent telemetry engine #40

Part of the core extraction (#35). Add the framework-independent telemetry engine and make the Angular services delegate to it.

Scope

• uwtCreateTelemetry(options) with scenarios, BI events, logging, setUserId, flush and an idempotent dispose().
• Browser features opt-in through document; no work on import, no global state.
• onSettled(listener) instead of an Observable, so the core's main entry needs no RxJS; the /rxjs entry for traceScenario.
• The Angular logger, BI and scenario services wrap the engine's concerns.

Done when

• The Angular package behaves as before; engine behaviour is covered by direct tests.