Fix package member resolution and improve find guidance

[richlander]

Summary

• unify package library/type resolution for member, type, and related package-backed commands
• fix bare --library selection inside multi-library packages like Microsoft.NETCore.App.Ref
• improve find follow-up guidance and skill docs so users carry forward package@version and library context
• bump the tool and embedded skill version to 0.7.6

Closes #307

Validation

• dotnet build src/dotnet-inspect/dotnet-inspect.csproj -c Release --configfile /Users/rich/git/dotnet-inspect/nuget.config
• dotnet build src/dotnet-inspect.Tests/dotnet-inspect.Tests.csproj -c Release -p:DefaultTargetFramework=net11.0 --configfile /Users/rich/git/dotnet-inspect/nuget.config
• dotnet /Users/rich/git/dotnet-inspect/artifacts/bin/dotnet-inspect.Tests/release/dotnet-inspect.Tests.dll -class "DotnetInspector.Tests.CommandExecutionTests"
• dotnet /Users/rich/git/dotnet-inspect/artifacts/bin/dotnet-inspect/release/dotnet-inspect.dll find RegexOptions --package Microsoft.NETCore.App.Ref --oneline
• dotnet /Users/rich/git/dotnet-inspect/artifacts/bin/dotnet-inspect/release/dotnet-inspect.dll member RegexOptions --package Microsoft.NETCore.App.Ref --library System.Text.RegularExpressions -v:q