Adds t_ssgi/s_ssgi bindings (group 2, bindings 5-6) to lighting_shadow_bind_group_layout and deferred_lighting.wgsl. Replaces the simple ambient term with SSGI-modulated ambient: ao*ssgi_ao applied to IBL diffuse+specular, plus ssgi_indirect for indirect color bleeding. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>