Add CLAUDE.md with project guidance for Claude Code

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Commands
+
+**Install:**
+```bash
+pip install -e .
+# With LocoMuJoCo support:
+pip install -e ".[loco-mujoco]"
+```
+
+**Run all tests:**
+```bash
+pytest
+```
+
+**Run a single test file:**
+```bash
+pytest tests/datasets/test_lafan1_csv_loader.py
+```
+
+**Run tests excluding slow/visual:**
+```bash
+pytest -m "not slow and not visual"
+```
+
+**Run visual tests (requires display):**
+```bash
+pytest --visualize -m visual
+```
+
+**CLI:**
+```bash
+iltools load loco_mujoco
+iltools load amass
+```
+
+## Architecture
+
+The package (`iltools`) is organized into four modules:
+
+### `iltools/core/`
+Foundational data types:
+- `Trajectory`: dataclass holding observations, actions, rewards, infos, and dt
+- `DatasetMeta`: Pydantic model describing a dataset (name, source, version, joint/body/site names, trajectory count and lengths)
+
+### `iltools/datasets/`
+All dataset I/O and management:
+- `BaseLoader` (abstract): defines the loader interface all concrete loaders implement
+- `Lafan1CsvLoader`: loads LAFAN1 motion capture CSVs; supports configurable input FPS, frame subsampling, and motion grouping
+- `LocoMuJoCoLoader`: integrates with the `loco-mujoco` library; supports multiple sub-datasets (default, LAFAN1, AMASS) and writes to Zarr
+- `TrajectoryDatasetManager` (`manager.py`): the main runtime class for RL training—manages a pool of pre-loaded trajectories across multiple parallel environments; supports assignment strategies (random, sequential, round-robin, curriculum) and uses compiled PyTorch functions for performance
+- `utils.py`: helpers to build TorchRL `TensorDictReplayBuffer` from Zarr datasets
+
+### `iltools/retarget/`
+Motion retargeting:
+- `BaseRetarget` (abstract): interface for retargeting implementations
+- `PinocchioRetarget`: kinematics-based retargeting using Pinocchio
+
+### `iltools/cli/`
+Typer-based CLI (`iltools` command). Commands map to dataset loaders; `retarget` is a placeholder.
+
+### Data Flow
+Datasets are stored on disk as **Zarr v3** archives. Loaders parse raw data (CSVs, loco-mujoco envs) and write Zarr. At training time, `TrajectoryDatasetManager` loads Zarr slices into TensorDicts for batched environment resets and trajectory tracking.
+
+## Test Markers
+- `slow`: long-running tests (skipped by default with `-m "not slow"`)
+- `visual`: tests that open a MuJoCo viewer (require `--visualize` flag to run)