Annotate makeCoordinator/makeUIView/updateUIView as @MainActor so reading
the @MainActor-typed onTick closure stays within MainActor isolation and
no longer triggers a Sendable conversion warning.
The Siri Remote's left/right d-pad only delivered a single discrete
seek per click — holding the button did nothing. A window-level custom
UIGestureRecognizer now tracks the actual press duration and drives a
repeating seek tick (10s → 20s → 30s acceleration) until release,
routing through the existing accumulating-seek paths so the scrubber
preview, debounced commit, and on-screen feedback all keep working.
