feat(render): Vulkan campaign V11 step 2 — delete the OpenGL backend

Vulkan is the sole, user-signed-off backend (V10 landed) and step 1
already removed ImGui/Studio/DevTools. This step deletes the GL
rendering backend itself: every Gpu/Gl/** implementation, the Wb
ManagedGL*/GLHelpers/GLSLShader/GLStateScope/RenderStateCache/
BindlessSupport family, Shader/ShaderProgramConstruction/SamplerCache,
RenderBootstrap, and RenderFrameGlStateController.

GameWindow.cs's Run()/CreateGraphics()/CreateBackbufferReader()/
OnLoad() collapse to their Vulkan-only arm; GameWindowGraphics loses
its OpenGlGameWindowGraphics subclass. RuntimeOptions.RenderBackend and
RenderBackendKind (incl. the Gl member of GpuBackendKind) are gone —
there is nothing left to select between. The five world-draw dual-arm
renderers (WbDrawDispatcher, EnvCellRenderer, TerrainModernRenderer,
ParticleRenderer, SkyRenderer) and the composition roots
(WorldRenderComposition, HostInputCameraComposition,
LivePresentationComposition, FrameRootComposition) collapse to their
RHI-only arm. GL-only diagnostic properties with a live external reader
(DynamicBufferCount and friends) simplify to a documented `=> 0`/no-op
rather than disappearing, since the reader is out of this commit's
scope.

A few GL-flavored mechanisms turned out to be backend-neutral once
isolated: GlConstructionCleanupLedger is renamed
ResourceConstructionCleanupLedger (exception-chain walking has nothing
to do with GL), and GlfwNativePlatformProbe moved out of the otherwise
GL-only GraphicalCapabilityRecord.cs into
GraphicalWindowBackendSelection.cs before the rest of that file was
deleted.

Test files with no surviving subject are deleted outright
(GraphicalCapabilityRequirementsTests, ShaderProgramConstructionTests,
PortalDepthShaderParityTests, TextureCacheBindlessTests,
TextRendererFailureSafetyTests, ClipFrameUploadTests, every
Gpu/Gl/*Tests, GlTextureOwnershipTests, RenderFrameGlStateControllerTests);
others get their dead GL-only members trimmed while their live
assertions stay (ClipFrameLayoutTests' MeshClipSsboBinding check now
reads GpuBindingModel.StorageClipRegions, the same binding index under
its new backend-neutral name; GpuResourceRetirementTransactionTests
drops its OpenGLGraphicsDevice-subclassing test double and the two GL
queue tests it existed for). EnvCellRendererTests' construction helper
now builds a real ObjectMeshManager via VulkanMeshPipelineDevice
instead of passing null through a null-forgiving operator, since the
RHI constructor never tolerated a null mesh manager and the old GL
constructor (which did) is gone.

Deferred to the next two steps, deliberately not touched here: the
Silk.NET.OpenGL/.Extensions.ARB package references, IMeshPipelineDevice.Gl
(WbMeshAdapter's GL? threading stays in place), Chorizite.Core's stale
csproj comment (the package itself is still load-bearing —
TextureFormat and friends are used well beyond the deleted
ManagedGLUniformBuffer), and the CI/gate scripts.

Build: `dotnet build AcDream.slnx -c Release` — 0 warnings, 0 errors.
Tests: full-solution `dotnet test` green across every project
(App.Tests 3937/3940 + 3 skips, Core.Tests 3296/3298 + 2 skips, all
others 100%); the 2 App.Tests names that flake under full-suite
parallel execution (#250-family, documented pre-existing) pass in
isolation.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/AcDream.App/Rendering/PaperdollFramePresenter.cs

@@ -1,7 +1,6 @@
 using System.Numerics;
 using AcDream.App.Input;
 using AcDream.App.Rendering.Gpu;
-using AcDream.App.Rendering.Gpu.Gl;
 using AcDream.App.UI;
 using AcDream.App.World;
 using AcDream.Content;
@@ -46,9 +45,9 @@ internal interface IPaperdollPoseApplicator
 }
 
 /// <summary>
-/// Owns paperdoll dirty/rebuild state and the private FBO presentation edge.
-/// The GL renderer remains a borrowed resource disposed by the existing window
-/// shutdown transaction.
+/// Owns paperdoll dirty/rebuild state and the private render-target
+/// presentation edge. The renderer remains a borrowed resource disposed by
+/// the existing window shutdown transaction.
 /// </summary>
 internal sealed class PaperdollFramePresenter : IPrivateEntityViewportFrame
 {