Use python3 as the canonical command name course-wide (#104) (#105)

modules/27-evals/lab/llm_judge.py

@@ -14,7 +14,7 @@ than pretending. NOTHING here pins a provider.
     EVAL_JUDGE_MODEL  # the model name to ask for
 
 Run it standalone to grade one sample:
-    python llm_judge.py "Add count command" "fix"
+    python3 llm_judge.py "Add count command" "fix"
 """
 
 import json

modules/27-evals/lab/run_eval.py

@@ -1,9 +1,9 @@
 """Run the eval set against one candidate and print a scorecard.
 
 Usage:
-    python run_eval.py candidates/current_model
-    python run_eval.py candidates/swapped_model
-    python run_eval.py candidates/current_model --threshold 0.9
+    python3 run_eval.py candidates/current_model
+    python3 run_eval.py candidates/swapped_model
+    python3 run_eval.py candidates/current_model --threshold 0.9
 
 A "candidate" is a directory containing a tasks.py that an agent produced. The
 runner imports that tasks.py, runs every case in eval_set.py against it, prints