Add error handling for 'mfc run' syntax

Address AI review feedback: prevent 'mfc run run case.py' issue by
detecting and rejecting the 'run' subcommand with a helpful error message.

If users try 'mfc run case.py', they now get:
  mfc (Homebrew): The 'run' command is not needed.
  Usage: mfc <case.py> [options]
  Example: mfc case.py -n 2

Author: sbryngelson

packaging/homebrew/mfc.rb

@@ -114,6 +114,14 @@ def install
           exit 0
         fi
 
+        # Check if user accidentally used 'mfc run' syntax
+        if [[ "${ARGS[0]}" == "run" ]]; then
+          echo "mfc (Homebrew): The 'run' command is not needed."
+          echo "Usage: mfc <case.py> [options]"
+          echo "Example: mfc case.py -n 2"
+          exit 2
+        fi
+
         # Always prepend "run" since this wrapper only supports running cases
         ARGS=("run" "${ARGS[@]}")