Add gumbel router configs sweeping learnable-knob combinations

Extends the 10-expert EnergyRouter + physical-conditioning benchmark
config with the new opt-in gumbel combine weights, isolating the
learn_centers/learn_temperature axis: none, centers only, and
centers+temperature.

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

configs/router_energy_n10_gumbel_centers_physical.toml

@@ -0,0 +1,22 @@
+[train]
+mode          = "flow"
+epochs        = 30
+lr            = 3e-4
+warmup_epochs = 3
+val_fraction  = 0.1
+num_workers   = 4
+
+[model]
+conditioning = "physical"
+dropout      = 0.0
+
+[model.router]
+enabled           = true
+type              = "energy"
+n_experts         = 10
+expert_hidden_dim = 128
+expert_n_blocks   = 4
+temperature       = 0.05
+lambda_balance    = 0.035
+learn_centers     = true
+gumbel            = true

configs/router_energy_n10_gumbel_centers_temp_physical.toml

@@ -0,0 +1,23 @@
+[train]
+mode          = "flow"
+epochs        = 30
+lr            = 3e-4
+warmup_epochs = 3
+val_fraction  = 0.1
+num_workers   = 4
+
+[model]
+conditioning = "physical"
+dropout      = 0.0
+
+[model.router]
+enabled           = true
+type              = "energy"
+n_experts         = 10
+expert_hidden_dim = 128
+expert_n_blocks   = 4
+temperature       = 0.05
+lambda_balance    = 0.035
+learn_centers     = true
+learn_temperature = true
+gumbel            = true

configs/router_energy_n10_gumbel_physical.toml

@@ -0,0 +1,22 @@
+[train]
+mode          = "flow"
+epochs        = 30
+lr            = 3e-4
+warmup_epochs = 3
+val_fraction  = 0.1
+num_workers   = 4
+
+[model]
+conditioning = "physical"
+dropout      = 0.0
+
+[model.router]
+enabled           = true
+type              = "energy"
+n_experts         = 10
+expert_hidden_dim = 128
+expert_n_blocks   = 4
+temperature       = 0.05
+lambda_balance    = 0.035
+learn_centers     = false
+gumbel            = true