Add CLAUDE.md file to project

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+This is a .NET Standard library for recursive DataAnnotations validation, extending the built-in validation capabilities to handle nested objects and collections within objects.
+
+The core functionality is provided by `RecursiveDataAnnotationValidator` which:
+- Validates an object graph recursively, traversing nested properties
+- Prevents infinite loops in cyclical object references
+- Supports `IEnumerable` collections for recursive validation
+- Allows skipping specific properties with `[SkipRecursiveValidation]` attribute
+
+## Project Structure
+
+The codebase has a clear separation between the main library and tests:
+
+1. **src/RecursiveDataAnnotationsValidation/** - The core library project with:
+   - Main validator implementation (`RecursiveDataAnnotationValidator.cs`)
+   - Skip attribute for excluding properties from validation (`SkipRecursiveValidation.cs`)
+   - Extension methods and interfaces
+
+2. **test/RecursiveDataAnnotationsValidation.Tests/** - Test project with:
+   - Tests for various recursive validation scenarios
+   - Example test models (RecursionExample, EnumerableExample, etc.)
+
+3. **examples/** - Example project showing usage patterns
+
+## Commands for Development
+
+### Build
+```bash
+dotnet build src/RecursiveDataAnnotationsValidation/RecursiveDataAnnotationsValidation.csproj
+```
+
+### Run Tests
+```bash
+dotnet test test/RecursiveDataAnnotationsValidation.Tests/RecursiveDataAnnotationsValidation.Tests.csproj
+```
+
+### Run Single Test
+```bash
+dotnet test test/RecursiveDataAnnotationsValidation.Tests/RecursiveDataAnnotationsValidation.Tests.csproj --filter "RecursionExampleTests.Passes_all_validation"
+```
+
+### Run Tests with Coverage
+```bash
+dotnet test test/RecursiveDataAnnotationsValidation.Tests/RecursiveDataAnnotationsValidation.Tests.csproj --collect:"XPlat Code Coverage"
+```
+
+## Key Files to Understand
+
+- `RecursiveDataAnnotationValidator.cs` - Main implementation that handles recursive object validation
+- `SkipRecursiveValidationAttribute.cs` - Attribute for excluding properties from recursive validation
+- Test models in `test/RecursiveDataAnnotationsValidation.Tests/TestModels/` show various usage patterns
+
+## Target Frameworks
+
+- Main library targets `.NET Standard 2.0`
+- Test project targets `net8.0`
+
+## Development Notes
+
+The recursive validator handles:
+1. Cyclical object references to prevent infinite loops
+2. Collections (IEnumerable) with recursive validation of items
+3. Null value handling for nested objects and collections
+4. Proper error message formatting that includes property paths
+
+The validator uses reflection to examine object properties and recursively validate nested objects.