Add CC0 PBRify ONNX models (#404)

1x-PBRify_Height.onnx

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+version https://git-lfs.github.com/spec/v1
+oid sha256:2b14afd583148cb5b0a554bf86a009b6a898aadc00d213aa3ec2544e17c835f5
+size 1640690

1x-PBRify_NormalV3.onnx

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+version https://git-lfs.github.com/spec/v1
+oid sha256:19d78f555f994219e2692876ab0fb6c3e4382503952dbe72d74db89d24870ba4
+size 1640690

1x-PBRify_RoughnessV2.onnx

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+version https://git-lfs.github.com/spec/v1
+oid sha256:8a8de1bbeab70df8b2550bdc11fddd5a315a12eeb47d561ce55b38551ea52131
+size 1640690

README.md

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+---
+license: cc0-1.0
+tags:
+  - onnx
+  - pbr
+  - texture
+  - normal-map
+  - qtmesheditor
+library_name: onnx
+---
+
+# QtMeshEditor — AI models
+
+ONNX models used by [QtMeshEditor](https://github.com/fernandotonon/QtMeshEditor)'s
+AI-assisted authoring features.
+
+## PBR map synthesis (issue #404)
+
+`1x-PBRify_NormalV3.onnx`, `1x-PBRify_RoughnessV2.onnx`, `1x-PBRify_Height.onnx`
+generate tangent-space normal / roughness / height maps from a single albedo
+(diffuse) texture.
+
+These are **ONNX re-exports** of the CC0 SPAN models from
+**[Kim2091/PBRify_Remix](https://github.com/Kim2091/PBRify_Remix)** (LICENSE:
+CC0-1.0), trained on CC0 content from ambientCG / Poly Haven. Converted with
+`scripts/export-pbrify-onnx.py` in the QtMeshEditor repo (spandrel +
+`torch.onnx.export`, opset 18). All credit for the weights goes to Kim2091.
+
+- **License:** CC0-1.0 (public domain), same as the source models.
+- **I/O:** 1×3×H×W float NCHW in `[0,1]` → 1×3×H×W out (normal as RGB;
+  roughness/height as RGB, consumed as luminance). Dynamic H/W.
+
+QtMeshEditor downloads these on first use into `<AppData>/ai_models/pbr/`.