refactor: clean up redundant patterns and reduce duplication

[everpcpc]

Summary

• Remove 211 redundant await MainActor.run wrappers across 53 files — SwiftUI Views and @MainActor ViewModels already run on MainActor, making explicit MainActor.run dispatching unnecessary inside Task {} blocks. 32 legitimate usages in actors/non-MainActor classes are preserved.
• Extract EllipsisMenuButton component to replace the repeated .hidden() + .overlay(Menu { ... }) hack pattern in 4 RowView files
• Merge duplicate CollectionViewModel/ReadListViewModel into a shared PaginatedIdViewModel that uses closure-based loading, eliminating two nearly identical 83-line files
• Consolidate 4 glassEffect methods into 2 using a GlassEffectType enum parameter
• Unify CompositeID usage — replace inline string interpolation with CompositeID.generate() in 2 store files
• Cache DateFormatter instances with static let in Date+Formatting to avoid per-call allocation
• Clean up dead code — remove empty prepareChapter stub, commented-out code, fix wrong file header

Net: 67 files changed, -506 lines

Test plan

• iOS build passes (make build-ios)
• macOS build passes (make build-macos)
• Manual test: browse collections and read lists (verifies PaginatedIdViewModel)
• Manual test: context menus on row views (verifies EllipsisMenuButton)
• Manual test: reader open/close (verifies MainActor.run removal)
• Manual test: cache clearing in settings (verifies MainActor.run removal)

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