Build a RendererCapabilities snapshot from a constructed
renderer. Call once after renderer init; pass the result to
consumers (PostProcessingManager, SceneManager, …).
framebufferYDown is computed by detectFramebufferYDown when
not supplied — that's the production path. Tests pass an explicit
value to skip the renderer-backend probe.
Build a
RendererCapabilitiessnapshot from a constructed renderer. Call once after renderer init; pass the result to consumers (PostProcessingManager, SceneManager, …).framebufferYDownis computed by detectFramebufferYDown when not supplied — that's the production path. Tests pass an explicit value to skip the renderer-backend probe.