fix: typos and nonexistent calls

configs/main_config.yaml

@@ -3,6 +3,7 @@
 # Sub-configs are loaded from the relative directories.
 
 defaults:
+  - brittle_star_config
   - experiment: base
   - logging: default
   - ppo: default

configs/ppo/smoke_test.yaml

@@ -0,0 +1,19 @@
+# Fast PPO Configuration
+# Lower timestep count for quick iterations/testing.
+
+learning_rate: 0.0005
+total_timesteps: 65536
+num_envs: 512
+num_steps: 128
+anneal_lr: true
+gamma: 0.99
+gae_lambda: 0.95
+num_minibatches: 4
+update_epochs: 4
+norm_adv: true
+clip_coef: 0.2
+clip_vloss: true
+ent_coef: 0.01
+vf_coef: 0.5
+max_grad_norm: 0.5
+target_kl: null