Add bigger WGAN config (hidden_dim=512, n_blocks=6)

Scaled-up variant of the already-trained wgan_h128_b4_physical.toml
benchmark config, same training recipe (mode/epochs/lr/warmup),
increased model capacity.

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

configs/wgan_h512_b6_physical.toml

@@ -0,0 +1,13 @@
+[train]
+mode          = "wgan"
+epochs        = 30
+lr            = 3e-4
+warmup_epochs = 3
+val_fraction  = 0.1
+num_workers   = 4
+
+[model]
+hidden_dim   = 512
+n_blocks     = 6
+dropout      = 0.0
+conditioning = "physical"