Native SharedWorker effects

Keep browser constructors in the browser

SharedWorker is now recognized as a native browser global. Inline effects can construct it and check availability without the compiler attempting to capture its value during build.

Existing port ownership

Ordinary effects own message listeners, port startup and cleanup. A real named SharedWorker regression verifies shared connections, leader handoff, conditional remount and unsupported-browser fallback. Public worker assets and coordination protocols remain application code.

Bounded compatibility

One global-list entry changes with no new runtime, pass or dependency. Relative TypeScript SharedWorker bundling and Vite sharedworker imports are outside this patch. The original Actual intake separately records a fresh-create coordination failure; whole-application multi-tab safety is not claimed. Generator 0.1.173 targets core ^0.17.12. No speed improvement is claimed.