This PR adds support for directory paths to the AddProject(string name, string projectPath) method, allowing users to specify a directory containing a .csproj file instead of requiring the full path to the project file.

Changes

• Enhanced AddProject method: Now accepts both file paths and directory paths
• Auto-discovery logic: When a directory path is provided, automatically searches for .csproj files
• Error handling: Provides clear error messages for edge cases (multiple files, no files found)
• Backward compatibility: Existing file path usage continues to work unchanged
• Comprehensive tests: Added tests covering all directory scenarios
• Updated documentation: Added examples showing both file and directory path usage

Usage Examples

Before (still supported):

builder.AddProject("app", "../PathToCode.Folder/PathToCode.Folder.csproj");

After (new functionality):

builder.AddProject("app", "../PathToCode.Folder");

This matches the behavior of AddNpmApp and AddPythonApp which also accept directory paths:

builder.AddNpmApp("app", "../pathToCode");
builder.AddPythonApp("app", "../pathToCode", "main.py");

Implementation Details

• If the path is a directory, searches for *.csproj files
• If exactly one .csproj file is found, uses it automatically
• If multiple .csproj files are found, throws DistributedApplicationException with file names listed
• If no .csproj files are found, throws DistributedApplicationException with clear message
• File paths continue to work exactly as before (100% backward compatible)

Testing

• All existing tests pass
• New tests cover:
  • Directory with single .csproj file ✅
  • Directory with multiple .csproj files (error case) ✅
  • Directory with no .csproj files (error case) ✅
  • File paths still work as before ✅
• Manual testing confirms all scenarios work correctly

Fixes #10439.

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