Configure NuGet package metadata and publishing workflow

[cursor]

Problem

Consumers must clone the repo and reference DBTools.dll manually. The project has no NuGet packaging metadata (PackageId, Version, Authors, Description, IsPackable).

Proposed solution

1. Add NuGet metadata to DBTools/DBTools.csproj
2. Document dotnet pack / install instructions in README
3. Optionally add a GitHub Actions workflow to publish on release tags

Suggested metadata fields:

• PackageId: e.g. DBTools.Sql or Gednt.DBTools
• Version: semantic versioning
• Authors, Description, PackageTags, RepositoryUrl
• IsPackable: true

Acceptance criteria

• dotnet pack produces a valid .nupkg
• README documents NuGet installation (local feed or NuGet.org)
• Optional: release workflow publishes packages

Notes

Provider packages (Npgsql, MySqlConnector, Microsoft.Data.Sqlite) should remain optional consumer dependencies, as today.