feat(bf16): BF16-tuned smoke test config + huber_delta TOML support
dqn-smoketest.toml: lr 3e-5→1e-5, gradient_clip 10→1,
huber_delta 10→1, q_clip ±200→±50, reward_scale 10→1,
noisy_sigma 0.5→0.3, spectral_norm 3→1.5
training_profile.rs: add huber_delta to TrainingSection + apply_to
Smoke test runs 3 epochs but Q-values diverge — C51 forward produces
overflow logits in bf16. Needs CUDA graph buffer size audit (graph
captured with F32 byte counts may have wrong bf16 sizes on replay).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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