fix: eliminate storyboard atlas overflow GPU stalls + bump framework to 2026.503.7 - #297

During gameplay load on Android Vulkan, DrawableStoryboard was creating a regular atlased TextureStore. Storyboard assets (large per-beatmap images) immediately exhaust the 2048×2048 atlas, producing 8+ overflow events in ~5 seconds — each allocating a fresh 16 MB GPU texture and firing a vkQueueSubmit, stalling the render thread. Confirmed in logs: all 8 overflows occur within the PlayerLoader entry window.

Changes

• DrawableStoryboard.cs — replace the per-storyboard TextureStore (atlased) with LargeTextureStore. Storyboard assets are large, single-use, per-beatmap images; atlas packing provides zero batching benefit and causes repeated overflow stalls. Also drops the incorrect scaleAdjust: 1 override that was forcing uploads at 1× physical resolution regardless of DPI.

// before
new TextureStore(host.Renderer, host.CreateTextureLoaderStore(
    CreateResourceLookupStore()
), false, scaleAdjust: 1)

// after
new LargeTextureStore(host.Renderer, host.CreateTextureLoaderStore(
    CreateResourceLookupStore()
))

LargeTextureStore : TextureStore, so [Resolved] TextureStore in DrawableStoryboardSprite / DrawableStoryboardAnimation continues to resolve correctly with no other changes needed.

• osu.Game/osu.Game.csproj, osu.Android.props, osu.iOS.props — bump ppy.osu.Framework / .Android / .iOS to 2026.503.7 (osu-framework pack run Support variable clockrates in Catch difficulty calculation #29, commit d522ff68), which picks up the framework-side LargeTextureStore changes.