Implement tile-based shadow map system (TBSM)

[Copilot]

Adds a full tile-based shadow map system to the forward renderer. The screen is divided into 16×16 pixel tiles; each tile carries a bitmask of which shadow lights affect it, so fragment shaders skip irrelevant shadow lookups entirely.

New components

• TileShadowPass – container (mirrors HizGenerator pattern) that owns:
  • A persistent Texture2DArray shadow atlas (1024×1024×MAX_SHADOW_LIGHTS=4, D32).
  • TileShadowPassInfo UBO – per-light view-projection matrix + type + position/radius.
  • Tile bitmask UBO – uint32_t[128×72] where bit N = shadow light N affects that tile.
  • CPU-side tile culling: directional lights mark all tiles; spot/point lights mark only tiles inside the projected screen-space bounding rect of their radius sphere.
• ShadowSlotPass – one RasterPass per active shadow light, rendering scene depth into its atlas layer via an imported ImageView.

Pipeline integration

DefaultForwardPipeline::Collect now calls tileShadow->Setup() first (to build shadow matrices before SetupGlobal reads LightMatrix), then tileShadow->AddPasses() to enqueue slot passes before the forward pass.

Four new descriptor bindings added to the default raster layout:

Binding	Name	Type
12	TileShadowInfo	UBO
13	TileLightBitmask	UBO
14	ShadowAtlas	Texture2DArray
15	ShadowAtlasSampler	Sampler

Shader integration

New assets/shaders/layout/tile_shadow.hlslh (auto-included via default_pass.hlslh) provides:

// In FSMain with ENABLE_TILE_SHADOW=1:
float shadow = ComputeTileShadow(input.Pos.xy, input.WorldPos);

ComputeTileShadow looks up the tile bitmask from SV_Position, then performs 3×3 PCF sampling from ShadowAtlas for each flagged light.

New ENABLE_TILE_SHADOW pragma option added to standard_pbr.hlsl alongside the existing ENABLE_SHADOW path.

Light system additions

• SpotLight::BuildShadowMatrix(SceneView&) – constructs a perspective shadow view from the spot light's position and cone direction.
• SpotLight: added SetPosition, SetDirection, SetRange, GetRange.
• LightFeatureProcessor::GetLights() – exposes the local light list for shadow light collection.

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