Add CLAUDE.md (#956)

### What does this PR do?

Add CLAUDE.md file with repo overview for AI agents


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Documentation**
* Added a comprehensive CLAUDE.md documenting the Model Optimizer:
concepts, architecture, design patterns and anti-patterns, security and
contribution guidelines, common commands, architecture layout, core
abstractions (modes), key components overview, CI/testing and export
guidance, setup and workflow tips, and links to further documentation.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Signed-off-by: Rohan Joshi <rohjoshi@nvidia.com>

Author: rohansjoshi

CLAUDE.md

@@ -0,0 +1,106 @@
+# CLAUDE.md
+
+NVIDIA Model Optimizer (ModelOpt): open-source library for model optimization techniques including
+quantization, pruning, distillation, sparsity, and speculative decoding to accelerate inference.
+Primarily Python codebase with optional C++/CUDA extensions supporting PyTorch, ONNX, and Hugging Face/Megatron models.
+
+> If a `CLAUDE.local.md` file exists alongside this file, read and respect it — it contains
+> developer-specific overrides that supplement this shared guidance.
+
+## Rules (Read First)
+
+**CRITICAL (YOU MUST):**
+
+- NVIDIA Apache 2.0 license header on ALL new Python/C++/CUDA files (see `LICENSE_HEADER`)
+- `git commit -s -S` (DCO sign-off + cryptographic signing required). Never attribute AI tools in
+  sign-off line
+- `pre-commit` hooks run on commit — if files are modified by hooks, re-stage and commit again
+- PRs require CODEOWNERS review (auto-assigned based on `.github/CODEOWNERS`)
+- After rebasing, always re-run tests locally before pushing
+- All code must follow the security guidelines in `SECURITY.md` — violations are blocked as pre-merge errors
+- For contribution guidelines, commit conventions, and PR requirements, see `CONTRIBUTING.md`
+
+## Common Commands
+
+| Task | Command |
+|------|---------|
+| Install (editable + dev) | `pip install -e ".[dev]"` |
+| CPU unit tests | `python -m pytest tests/unit` |
+| GPU unit tests | `python -m pytest tests/gpu` |
+| Megatron GPU tests | `python -m pytest tests/gpu_megatron` |
+| TRT-LLM GPU tests | `python -m pytest tests/gpu_trtllm` |
+| Pattern match | `pytest tests/unit -k "test_quantize"` |
+| Lint + format (all files) | `pre-commit run --all-files` |
+| Lint (diff only) | `pre-commit run --from-ref origin/main --to-ref HEAD` |
+| Run via tox (CPU unit) | `tox -e py312-torch210-tf_latest-unit` |
+| Build docs | `tox -e build-docs` |
+| Build wheel | `tox -e build-wheel` |
+
+## Architecture
+
+ModelOpt is organized into three top-level namespaces:
+
+| Namespace | Path | Role |
+|-----------|------|------|
+| `modelopt.torch` | `modelopt/torch/` | Core PyTorch optimization library |
+| `modelopt.onnx` | `modelopt/onnx/` | ONNX model quantization and export |
+| `modelopt.deploy` | `modelopt/deploy/` | Deployment utilities for LLMs |
+
+### `modelopt.torch` Sub-packages
+
+| Sub-package | Path | Role |
+|-------------|------|------|
+| `opt` | `modelopt/torch/opt/` | Core optimization infrastructure (modes, config, state dicts) |
+| `quantization` | `modelopt/torch/quantization/` | PTQ, QAT, and quantization-aware algorithms |
+| `prune` | `modelopt/torch/prune/` | Structured and unstructured pruning |
+| `distill` | `modelopt/torch/distill/` | Knowledge distillation |
+| `sparsity` | `modelopt/torch/sparsity/` | Weight and activation sparsity |
+| `speculative` | `modelopt/torch/speculative/` | Speculative decoding (Medusa, EAGLE, etc.) |
+| `nas` | `modelopt/torch/nas/` | Neural architecture search |
+| `export` | `modelopt/torch/export/` | Checkpoint export for TRT-LLM / Megatron |
+| `peft` | `modelopt/torch/peft/` | QLoRA and PEFT integration |
+| `_deploy` | `modelopt/torch/_deploy/` | Internal deployment utilities |
+| `utils` | `modelopt/torch/utils/` | Shared utilities and plugin infrastructure |
+
+### Core Abstraction: Modes
+
+A **mode** is the unit of model optimization in ModelOpt. Each algorithm (quantization, pruning,
+etc.) is implemented as one or more modes. Modes are recorded in the model's `modelopt_state` so
+optimization workflows can be composed, saved, and restored.
+
+## Key Files
+
+| File | Role |
+|------|------|
+| `modelopt/torch/opt/mode.py` | Base class for all optimization modes |
+| `modelopt/torch/opt/config.py` | Configuration system for modes |
+| `modelopt/torch/opt/conversion.py` | `apply_mode()` / `restore()` entry points |
+| `modelopt/torch/quantization/__init__.py` | PTQ/QAT public API |
+| `modelopt/torch/export/unified_export_hf.py` | Unified HF checkpoint export |
+| `modelopt/torch/export/model_config_export.py` | TRT-LLM model config export |
+| `modelopt/deploy/llm/` | LLM deployment utilities |
+| `pyproject.toml` | Optional dependency groups (`[onnx]`, `[hf]`, `[all]`, `[dev]`); ruff, mypy, pytest, bandit, and coverage config |
+| `.pre-commit-config.yaml` | Pre-commit hooks (ruff, mypy, clang-format, license headers) |
+| `tox.ini` | Test environment definitions |
+
+## Design Patterns
+
+| Pattern | Key Points |
+|---------|------------|
+| **Mode composition** | Optimization algorithms are composed as sequences of modes, each recorded in `modelopt_state` |
+| **Plugin system** | Optional integrations (HuggingFace, Megatron, etc.) loaded lazily via `import_plugin()` |
+| **Optional dependencies** | Features gated by install extras (`[onnx]`, `[hf]`, `[all]`); avoid hard imports at module level |
+| **Config dataclasses** | Each mode has a typed config; use Pydantic or dataclass conventions |
+| **State dict** | Models carry `modelopt_state` for checkpoint save/restore across optimization steps |
+
+## CI / Testing
+
+| Layer | Location | Notes |
+|-------|----------|-------|
+| CPU unit tests | `tests/unit/` | Fast, no GPU needed; run in pre-merge CI |
+| GPU unit tests | `tests/gpu/` | Requires CUDA GPU |
+| Megatron GPU tests | `tests/gpu_megatron/` | Requires Megatron-Core + GPU |
+| TRT-LLM GPU tests | `tests/gpu_trtllm/` | Requires TensorRT-LLM + GPU |
+| Example/integration tests | `tests/examples/` | Integration tests for examples; see `tests/examples/README.md` |
+| Pre-commit / lint | `.pre-commit-config.yaml` | ruff, mypy, clang-format, license headers, bandit |
+| Coverage | `pyproject.toml` | 70% minimum on `modelopt/*` |