docs: add Write Tests and Run Validation critical rules (#36)

Author: CalvinAllen

CLAUDE.md

@@ -15,8 +15,10 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 7. **Check branch status before pushing** - Verify the remote tracking branch still exists. If a PR was merged/deleted, create a new branch from main instead
 8. **Microsoft coding guidelines** - Follow [Microsoft C# coding conventions](https://learn.microsoft.com/en-us/dotnet/csharp/fundamentals/coding-style/coding-conventions) and [.NET library design guidelines](https://learn.microsoft.com/en-us/dotnet/standard/design-guidelines/)
 9. **WPF for all UI** - All UI must be implemented using WPF (XAML/C#). No web-based technologies (HTML, JavaScript, WebView)
-10. **No co-authors** - Do not add co-author information on commits or pull requests
-11. **No "generated by" statements** - Do not add generated-by statements on pull requests
+10. **Write tests** - All new/refactored code requires tests where applicable
+11. **Run validation before commits** - Run `dotnet build` and verify no errors before committing
+12. **No co-authors** - Do not add co-author information on commits or pull requests
+13. **No "generated by" statements** - Do not add generated-by statements on pull requests
 
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