S4a-3b of the PlexPlayer decomposition. Move the intro/credits auto-skip
machinery (activeMarker detection, the skipProgress countdown, doSkip,
cancelAutoSkip + the running-interval and reset-on-id effects) into
useAutoSkip. The hook returns skipProgressRef / cancelAutoSkipRef — the
forward-declaration bridge the earlier keyboard/back handlers read to
cancel a running countdown; those two stable refs are now listed in the
backIntent/keyboard dep arrays (they were provably-stable local refs
before, params now). No behaviour change; verified by self-E2E (credits
marker detected -> countdown fill renders + advances while playing ->
auto-skip fires -> item marked Watched + player closes).
peter
521d2aeaa8