feat(references): update project references after rename

[CalvinAllen]

Summary

• Adds ProjectReferenceService to manage project references during rename operations
• Before removing the project, collects all projects that have a <ProjectReference> to it
• After rename, updates those references with the new project path
• Handles both SDK-style and legacy (MSBuild namespace) project files

How it works

1. Before removal: Scans all projects in solution to find those referencing the target
2. After file/directory rename: Updates <ProjectReference Include="..."> paths in those projects
3. Calculates correct relative paths from each referencing project to the renamed project

Test plan

• Rename a project that is referenced by another project
• Verify the referencing project's .csproj is updated with new path
• Verify solution still builds after rename
• Test with projects in different directory depths

Closes #23