build(deps): centralize NuGet package versions

[nmummau]

Move all 34 package versions into Directory.Packages.props, preserving
existing versions and project-specific metadata.

Scope the framework reference entry to SSMS to avoid conflicting with
the installer's implicit SDK reference.

Update CI cache inputs and deployment triggers for the central file.

What does this PR do?

Centralizes all 34 NuGet package versions in Directory.Packages.props, making dependency updates easier to manage while preserving existing versions and project settings.

Limits the framework reference entry to SSMS because the installer gets that package automatically from the .NET SDK. Updates automated builds and deployments to recognize changes to the central package file.

Which component(s) does this affect?

• Desktop App (PlanViewer.App)
• Core Library (PlanViewer.Core)
• CLI Tool (PlanViewer.Cli)
• SSMS Extension (PlanViewer.Ssms)
• Tests
• Documentation

Also affects the Web App, PlanShare server, and shared build configuration.

How was this tested?

On Linux:

• Release builds of the solution, PlanShare server, and SSMS installer passed with zero warnings.
• SSMS extension package restore passed; its full Windows build was not tested.
• Verified central package management across all eight projects and confirmed existing package versions and reference settings were
  preserved.

Tests were not run, and no plan files were tested. This change only reorganizes package configuration.

Checklist

• I have read the contributing guide (https://github.com/erikdarlingdata/PerformanceStudio/blob/main/CONTRIBUTING.md)
• My code builds with zero warnings (dotnet build -c Debug)
• All tests pass (dotnet test)
• I have not introduced any hardcoded credentials or server names