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fix(signals): tracked effect re-runs for a same-pass write (#4598) (#4602)

* fix(signals): tracked effect re-runs for a same-pass write (#4598)

A createTrackedEffect links its dependencies in the effect phase, so a
signal written earlier in that phase (another effect's first run, a
parent's onSettled writing a prop) had already walked its subscribers
before the tracked effect linked to it. The read served the committed
value (A32), the commit at the next seam notified nobody, and the effect
never ran with the new value; createEffect(compute, fn) links at creation
and saw it.

After a tracked effect's run, a dependency staged this flush for its seam
to commit whose subscriber walk (its notify-epoch stamp) predates the run
re-queues the effect on the heap, so it runs again in the round that
commits the staging. A write of the pass's own walked after the run began
and keeps the #3006 contract (never observed, no re-run); onSettled reads
untracked, links nothing, and stays one-shot. The check lives in the
tracked effect's own runner, so bundles without createTrackedEffect or
onSettled pay nothing. The test that pinned the gap now pins the re-run.

* fix: address review findings

A tracked effect no longer re-runs for a dependency whose staged value
nets to the committed value (`setS(1); setS(0)` on a committed 0), using
the same `===` and `Object.is` netted test as the other staged-read
paths. The post-run dependency walk is skipped when nothing is staged in
the flush (`pendingNodes` is empty), which is the case for every run the
commit already notified. The comment above the walk is cut to one line.

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