feat: unify Blender rendering quality with shape-completion Renderer and blender_load.py

[hummat]

Context

Multiple Blender rendering codepaths exist across projects. bproc-pubvis has the best lighting, backdrop, and publication defaults, but lacks some features found in other rendering approaches. Goal: unify correctness and quality.

Missing features

Camera

• Custom K-matrix intrinsics: Some renderers accept custom camera intrinsic matrices for precise camera control. bproc-pubvis uses location-based camera setup only.

Output

• Normal maps: Other renderers output color, depth, and normal maps natively. bproc-pubvis outputs color and optional depth compositing but no normal maps.
• Multi-engine fallback: Some renderers support Cycles, EEVEE, PyRender, Open3D, PyTorch3D with automatic fallback. bproc-pubvis supports Cycles and EEVEE only.

Point clouds

• Auto-radius from density: Other approaches compute per-point radius via KDTree nearest-neighbor with density-aware floors, handling varying point densities gracefully. bproc-pubvis uses fixed instance sizing.
• Density-aware subsampling: Other approaches support both destructive and runtime subsampling with density floors. bproc-pubvis has FPS subsampling but no density-aware floors.

Materials

• Product-style materials: Some renderers use Principled BSDF with coat weight, coat roughness, and specular level for product-style shots. bproc-pubvis uses preset-based materials which are good but less fine-tunable.

Strengths to preserve

• Publication-ready defaults (Filmic, Medium Contrast, OptiX→OIDN denoiser)
• Structured lighting (key/fill/rim) with configurable intensity
• Shadow presets (VERY_HARD→VERY_SOFT)
• Shadow catcher backdrop, HDRI support, transparent gradients
• Animation support (orbit, tumble, gravity)
• CLI-driven dataclass config
• Enum-based presets (Look, Shadow, Light, Shape) for reproducibility