Prepare the NuGet package: metadata, readme, icon, SourceLink, symbols

[vaceslav]

dotnet pack already produces a single TriasDev.Tabular package, but it carries only the basics from src/Directory.Build.props.

• Description and PackageTags — describe it by what it reads (csv, excel, xlsx, import, parsing, schema-mapping); avoid a bare tabular tag, which on NuGet means Analysis Services / Power BI models
• PackageProjectUrl, RepositoryUrl, RepositoryType
• PackageReadmeFile (root README.md)
• PackageIcon — assets/icon.svg, PNG exports; option A
• SourceLink, IncludeSymbols + SymbolPackageFormat=snupkg, ContinuousIntegrationBuild in CI, deterministic build
• Inspect the produced .nupkg (contents, XML docs, readme rendering)

[vaceslav]

From the pre-release review (packing and inspecting the current .nupkg):

• Description is the SDK placeholder "Package Description"; set Description and PackageTags (csv, excel, xlsx, import, parser, schema-mapping, data-profiling; no bare tabular).
• No repository/project URL, readme or icon. Ship a package-specific README — the repo README has relative links that 404 on nuget.org.
• Symbols: IncludeSymbols + SymbolPackageFormat=snupkg, PublishRepositoryUrl, EmbedUntrackedSources, ContinuousIntegrationBuild in CI (a local PDB currently embeds absolute /Users/… paths).
• EnablePackageValidation now; a baseline version after the first release.
• Public API tracking with Microsoft.CodeAnalysis.PublicApiAnalyzers (PublicAPI.Shipped/Unshipped.txt) after Reshape the public API before the first release #15 settles the surface.
• IsAotCompatible=true (implies trimmable): the trim/AOT analyzers already report 0 warnings.
• Record the decisions: no strong naming; no analyzer packages leak as dependencies (verified).

[vaceslav]

Done in ceb13f9, except the icon.

• Metadata: description, tags (no bare tabular), project and repository URLs, README in the package. README links are now absolute, so they work on nuget.org.
• Symbols and builds: SourceLink metadata (the nuspec records the commit), a .snupkg, deterministic builds, and ContinuousIntegrationBuild under GitHub Actions.
• API freeze from Reshape the public API before the first release #15: PublicApiAnalyzers with 1,013 members in PublicAPI.Unshipped.txt (RS0016/RS0017 fail the build), and EnablePackageValidation. The baseline version is set once 0.1.0 is published.
• Package check: net8.0 and net10.0 with XML docs and no dependencies. A fresh net8 console app installed it from a local source and ran the README quick start, including the import. Output matched.

Open: PackageIcon. None exists yet; see assets/ in templify for the shape.

[vaceslav]

The icon is in (option A: a table in the Templify document), under assets/, and packed as icon.png. Every item is done.