Add giant new-run to scaffold a config.toml + run dir ahead of training

Pulled forward from the not-yet-mergeable condor-gpu-train-rollout branch:
`new-run` resolves CLI hyperparameter overrides into a full config.toml and
run dir (reusing the existing default_out_dir_name collision-avoidance and a
newly factored-out router-override helper shared with `train`), so a run can
be prepared and reviewed before `giant train` actually kicks off. Also
brings README up to date with the model/CLI as it actually stands
(physical/embedding conditioning, WGAN/MoE-router modes, giant analyze,
W&B, setup-stage caching), which had drifted back to describing the
Phase-1 proof-of-concept.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

CLAUDE.md

@@ -10,6 +10,7 @@ uv sync --extra cuda               # install dependencies with CUDA 11.8 torch
 uv sync --extra cpu --extra dev    # add dev extras (pytest, etc.)
 uv sync --extra cpu --extra geometry  # add scikit-learn for the geometry oracle (giant rollout)
 pytest               # run tests
+giant new-run --hidden-dim 512 --lr 3e-4        # scaffold a config.toml + run dir ahead of training
 giant train path/to/steps.parquet --mode flow   # train (flow matching)
 giant train path/to/steps.parquet --mode ddpm   # train (DDPM baseline)
 giant train path/to/steps.parquet --mode wgan   # train (WGAN-GP, single-pass eval; implemented, not yet tested)