Issue 1.1: Setup OpNode.Core and Test Projects

[marcnoon]

Issue 1.1: Setup OpNode.Core and Test Projects
Epic reference: This issue is part of the parent epic: Epic: Establish Testable Core Architecture: Validation, Operations, and Serialization (#64)

Objective
Set up the foundational structure for all business logic and testing for OpNode, strictly decoupled from any UI dependencies.

Tasks
Create OpNode.Core as a class library to contain all business logic.
Create OpNode.Core.Tests as a unit test project.
Ensure OpNode.Core does NOT depend on System.Windows.Forms or any UI-related libraries.
In OpNode.Core, define:
A base service: NamingValidator
A result structure: ValidationResult
Add at least one sample unit test in OpNode.Core.Tests to demonstrate the setup.
Acceptance Criteria
Both projects exist, build successfully, and OpNode.Core is free of UI dependencies.
NamingValidator and ValidationResult are implemented.
At least one example unit test passes in OpNode.Core.Tests.
All work is referenced back to this issue and the parent epic.
This structure provides a clear checklist and context for any developer or Copilot agent working on the issue. Let me know if you want a variant or want to include further details!