Add Plot Profile command

[yangfei]

Summary

• Add core profile calculation for horizontal center lines.
• Define first supported sources as full-image center line or active rectangle ROI center line.
• Add Analyze > Plot Profile and a simple plot window.
• Add core tests for full-image and rectangle ROI profile values.

Verification

• dotnet build ImageJCsharp.sln
• dotnet test tests/ImageJCsharp.Core.Tests/ImageJCsharp.Core.Tests.csproj
• dotnet test tests/ImageJCsharp.App.Tests/ImageJCsharp.App.Tests.csproj

Closes #18