Add DependencyInjection.Sample demonstrating RegisterDi

[Skymly]

Summary

Add a runnable DependencyInjection.Sample that demonstrates generated RegisterDi for Strategy, Factory, and Handler pipelines using DesignPatterns.Extensions.DependencyInjection.

Acceptance criteria

• New sample under samples/DependencyInjection.Sample/ referenced from DesignPatterns.slnx
• Program.cs builds ServiceCollection, calls RegisterDi, resolves registries/pipeline, prints results
• Sample references DI package, generator, and DesignPatterns.Extensions.DependencyInjection.targets
• Nuke BuildSamples / CI continues to build the new sample
• Brief mention in README.md or docs/DEVELOPMENT.md

Module

samples/ only