Add server-driven featured spotlight on mobile

[blurbery]

Summary

• turn the first Home row into the iOS mobile hero only when that exact row is marked Featured and contains items
• leave Featured rows further down Home as ordinary mobile rows, so multiple Featured rows cannot replace or scramble the hero
• use a full-bleed backdrop, centered movie/show logo with title fallback, centered metadata and overview, plus Play / More Info actions
• auto-advance every 10 seconds and support direct swipe gestures, with no on-screen arrows or slide controls
• route Play through the existing playback flow so the profile's configured playback quality is respected
• prefetch featured logos and backdrops for smoother first paint
• hide every Featured row on tvOS while leaving its existing hero/layout unchanged

Platform scope

• iOS receives the new mobile spotlight.
• tvOS receives no hero redesign; it only stops rendering redundant Featured rows.
• macOS behavior is unchanged.

Validation

• 11 focused Home section tests passed with 0 failures, including top-row promotion, lower Featured-row retention on mobile, and Featured-row suppression on tvOS.
• Signed iPhone 17 Pro simulator build passed on Xcode 26.6 / iOS 26.5.
• Authenticated simulator verified artwork bleed, centered logo/content, Play / More Info placement, swipe gestures, and complete timed transitions without a stuck half-swipe.
• A separate tvOS compile is unavailable locally because the tvOS 26.5 Xcode component is not installed.

Previews

Internal fork review PR. After approval, this focused branch can be submitted separately to Silo-Server/silo-apple:main.