Native iPad interface: sidebar navigation + responsive grids

[MoreBlood]

Summary

Adapts AltStore for iPad with a native sidebar and width-responsive grids, without changing the iPhone UI — everything is gated on idiom / size class / a max content width, so compact widths are untouched.

Screenshots

iPad Pro, landscape — the tabs become a native sidebar tiled beside the content.

News	Sources (centered empty state)

Add Source	Browse

App detail	My Apps

Settings

What changed

• Sidebar (TabBarController) — on iPad (iOS 18+) the tabs render as a native sidebar (UITabBarController.mode = .tabSidebar) tiled beside the content; iPhone keeps the bottom tab bar. Deep links / programmatic selection use identity-based UITab lookup when the sidebar is active.
• My Apps — the storyboard flow layout is replaced with a UICollectionViewCompositionalLayout so the installed-apps grid has exactly even gaps and adapts its column count to width (1 on iPhone, 2–3 on iPad). Update cards stay self-sizing; section headers / App IDs footer are reproduced as boundary supplementary items.
• Sources — compositional adaptive grid + centered empty-state ("What are sources?") text.
• Browse — more columns / wider cards at regular width.
• News — feed constrained to a centered readable column; footer banner width matched to the news cards.
• Detail pages — shorter hero at regular width.
• Project — TARGETED_DEVICE_FAMILY = "1,2" on the app target.

Testing

• Built and run on the iPad simulator (iPad Pro 13"). Sidebar tiles in landscape, collapses to a top strip in portrait; grids reflow on rotation / sidebar toggle. iPhone tab bar unchanged.

Notes for review

• Minimum iOS for the sidebar: the .tabSidebar presentation is iOS 18+; on iPad running iOS 17 the app falls back to the existing tab bar.
• Drag-to-reorder active apps when there are no inactive apps — the drop delegate reads both section headers' attributes; the new layout only creates the "Inactive" header when that section is populated (same as the old .zero behavior). Happy to add an invisible anchor header if you'd prefer that be unconditional.