Add comprehensive integration test scripts for Cast Tool self-analysis

[Copilot]

This PR creates comprehensive integration test scripts that compile the Cast Tool project to an executable and use it to analyze and modify a copy of its own codebase, verifying that expected changes occur.

What's Added

Test Scripts

• test-simple.sh - Clean, focused bash script demonstrating core functionality
• test-simple.ps1 - PowerShell equivalent for Windows users
• test-integration.sh - Comprehensive test script with extensive validation

Cross-Platform Support

Both bash and PowerShell versions ensure the tests work on Linux, macOS, and Windows environments.

How It Works

All test scripts follow the same workflow:

1. Build - Compile the Cast Tool executable in Release mode
2. Copy - Create a temporary copy of the codebase for safe testing
3. Analyze & Modify - Apply various refactoring operations:
   • Add using statements (System.Text.Json)
   • Convert methods to properties (getValue() → Value property)
   • Sort using statements alphabetically
   • Analyze code symbols and dependencies
4. Verify - Confirm expected changes occurred and modified copy still builds
5. Cleanup - Remove temporary files

Example Output

$ ./test-simple.sh

=== Cast Tool Self-Analysis Integration Test ===
[SUCCESS] ✅ Cast Tool built successfully
[SUCCESS] ✅ Created test copy
🧪 TESTING CAST TOOL FUNCTIONALITY ON COPY
[SUCCESS] ✅ Successfully added using statement
[SUCCESS] ✅ Successfully converted method to property  
[SUCCESS] ✅ Using statements sorted
[SUCCESS] ✅ Modified copy builds successfully!
🎉 Integration test completed successfully!

Documentation Updates

Updated the README with a new Testing section that explains how to run the integration tests and what they demonstrate.

The tests prove the Cast Tool works correctly by successfully analyzing and modifying a copy of its own C# codebase, showcasing the tool's self-hosting capabilities.

Fixes #9.

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