Platform roadmap research: Steam Deck, Android, iOS, Web #100

Goal

Decide which platforms beyond Windows, Linux and macOS (#73, #74) Turian targets, and in what order, with the cost of
each written down.

Questions per platform

• Steam Deck / SteamOS: already Linux + Vulkan; mostly verification and controller-first UX
• Android: .NET for Android, Vulkan availability, texture formats (ASTC/ETC2, see the per-target texture variants
  in the importer), touch input, APK/AAB export
• iOS: NativeAOT, MoltenVK (shared with Epic: plugin and package system (manifest, discovery, Package Manager, registry) #74), signing, App Store rules
• Web: WebAssembly + WebGPU, no Vulkan; implies the RHI work (Implement shadow mapping for lights #39)
• Consoles: NDA platforms, NativeAOT requirements; out of scope until there is a partner

Deliverable

A decision record and one issue per chosen platform.