Implement shadow mapping for lights #39

Implement shadow mapping for directional and point lights.

Parent Issue

Part of the 3D scene pipeline improvements.

Current State

No shadow casting exists. Lighting is PBR (Cook-Torrance GGX in standardShader.frag) with point and directional lights, all unshadowed.

Tasks:

• Implement shadow map rendering pass (depth pre-pass from light perspective)
• Add shadow map textures (VkImage with depth format)
• Implement shadow comparison in the fragment shader (PCF filtering)
• Support directional light cascaded shadow maps (CSM)
• Support point light shadows (cube map or dual-paraboloid)
• Add shadow settings to light components (bias, resolution, cascade count)
• Implement shadow debug visualization in Scene View

Acceptance Criteria:

• Directional lights cast hard and soft shadows.
• Point lights cast omnidirectional shadows.
• Shadow artifacts (acne, peter-panning) are controllable via bias settings.
• Shadow settings are configurable per-light in the Inspector.

Related:

• Implement post-processing pipeline #40 (Standard Library Components — light components)
• Implement shadow mapping for lights #39 (RHI — depth texture abstraction)