[Feature]: Add `Directory.Build.props` for shared metadata

[samatstariongroup]

Prerequisites

• I have written a descriptive issue title
• I have verified that I am running the latest version of the EcoreNetto
• I have searched open and closed issues to ensure it has not already been reported

Description

• Summary: Company, Copyright, Authors, license expression, repository URL, and SourceLink settings are duplicated across every .csproj. There is no Directory.Build.props.
• Affected files: repo root (new Directory.Build.props); all */*.csproj.
• Proposed solution: Create Directory.Build.props with the common metadata and remove the duplicated properties from individual projects, leaving only project-specific values (package id, description, version per D6).
• Acceptance criteria:
  • Shared metadata lives in Directory.Build.props; projects no longer repeat it.
  • dotnet build and packaging still produce the same metadata.