[proxy] add rtk dotnet wrappers for run, ef, user-secrets, nuget, tool

Use case

For .NET developers using Claude Code, dotnet build/test/restore/format are already proxied. The following subcommands are equally output-heavy but lack proxies:

Subcommand	Why it's noisy
dotnet run	Build banner + application stdout/log noise
dotnet ef …	"Build started…/Build succeeded" header + verbose migration info
dotnet user-secrets list	JSON dump with whitespace
dotnet nuget list/search	Padded tables
dotnet tool list	Padded tables

Frequency (30-day Claude Code history via rtk discover)

• dotnet run: 39
• dotnet user-secrets: 36
• dotnet ef: dominant in EF-Core-heavy projects (not in default discover sample but ubiquitous in .NET stacks with migrations)

Suggested approach

A shared MSBuild-banner stripper plus per-subcommand filters analogous to rtk dotnet build. The ef filter should also strip the duplicate build preamble that EF emits before the actual migration output.