[Infra] contracts/fix_args.py has no docstring or usage instructions

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Why this matters
contracts/fix_args.py exists at the contracts root with no comment explaining when or why it should be run, so it is unclear if it is a one-off migration helper or part of a repeatable workflow.

Acceptance criteria

• Add a module docstring to fix_args.py explaining its purpose and invocation
• Note in contracts/README.md whether it is a one time script or should be re-run

Files to touch

• contracts/fix_args.py
• contracts/README.md

Out of scope
Rewriting the script's logic.