Fix hero carousel freezing while Home is covered/backgrounded

[imbenjamin]

Summary

Fixes a bug (found while manually testing, unrelated to the trickplay work in #87) where Home's hero carousel dot indicator keeps advancing on its own, but the visible backdrop/logo content freezes on whatever item was showing when the carousel was last covered — e.g. after opening and closing the Player, or pushing into a detail screen and popping back.

Root cause

HeroRailView's auto-advance tickTimer isn't gated on the view's on-screen visibility. Because a pushed detail screen (and the Player, presented via .fullScreenCover from there) sits above Home in the same NavigationStack, Home stays mounted underneath rather than being torn down — so the timer keeps ticking and writing to the scrollPosition state var (which the dot indicator is a pure function of) the whole time it's covered. The real backing UIScrollView can't actually move itself while off-screen/detached, though, so it silently stays wherever it last was. Nothing reconciles the two once Home becomes visible again — until a real touch-driven swipe happens to force a resync, which is what made it look "fixable by swiping."

Fix

Wrap the paging ScrollView in a ScrollViewReader and force a real, animation-free proxy.scrollTo(_:anchor:) to the current scrollPosition in .onAppear — the same nudge a manual swipe was giving it for free, now applied automatically the instant Home becomes visible again.

Verification

• Live-reproduced the original bug on the Simulator (screenshots of the dot advancing while content stayed frozen), confirmed a manual swipe "unstuck" it.
• Rebuilt with the fix, reproduced the same cover/return sequence (push into a detail screen, wait through a couple of auto-advance ticks, pop back) — hero content now matches the dot immediately, no manual nudge needed, and auto-advance keeps running smoothly afterward.
• Full test suite: 469 tests passing.

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