Add CLAUDE.md for Claude Code guidance

[ElanHasson]

Summary

• Adds comprehensive CLAUDE.md documentation for Claude Code
• Includes build commands, architecture overview, and integration details
• Documents the fluent builder pattern and core components
• Provides package management and Temporal integration guidance

Details

This PR adds a CLAUDE.md file to help future Claude Code instances work more effectively in this repository. The documentation includes:

1. Build and Development Commands - Essential dotnet commands for building, packing, running samples, and managing packages
2. Architecture Overview - Detailed explanation of the dual deployment model (Container vs Executable), key classes with file references, fluent builder pattern, and configuration enums
3. Project Structure - Layout of library and sample projects with dependencies
4. Temporal Integration - Connection string handling, observability setup, and endpoint configurations
5. Package Management - Notes about NuGet packaging and versioning

The documentation focuses on architectural patterns that require understanding multiple files and provides specific file/line references for efficient navigation.

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