[Feature]: Add `Directory.Packages.props` (central package management)

[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: NuGet package versions are repeated across 6+ projects (Serilog, NUnit, coverlet, Moq, SourceLink, etc.), inviting version drift.
• Affected files: repo root (new Directory.Packages.props); all */*.csproj PackageReference version attributes.
• Proposed solution: Enable Central Package Management (ManagePackageVersionsCentrally=true) with <PackageVersion> entries in Directory.Packages.props; strip Version= from project references.
• Acceptance criteria:
  • All package versions are defined centrally.
  • Solution restores and builds unchanged.