React18 Legacy Context

If you're staring down legacy React context code with contextTypes and getChildContext, this walks you through the full migration to createContext without breaking your app in the process. The key insight here is that context migration is inherently cross-file work: you can't just update the provider or just update the consumers, you have to coordinate both or everything breaks at runtime. It gives you the exact grep commands to find all providers and consumers, then a strict ordering of steps to prevent the most common mistake (missing a consumer somewhere). Includes reference files for single context, multiple contexts, and a template for the new context module structure.