Add Ports and Adapters architecture pattern

[JerrettDavis]

Pattern

Expose first-class hexagonal architecture support for driving ports, driven ports, adapters, and composition roots.

Family

ApplicationArchitecture

Acceptance criteria

• Add a fluent/runtime API in src/PatternKit.Core using existing PatternKit naming and builder conventions.
• Add a source-generated path with attributes in PatternKit.Generators.Abstractions and generator support in PatternKit.Generators.
• Cover runtime, generator, diagnostics, and examples with TinyBDD scenarios and assertion trees.
• Add a real-world, importable example that works with IServiceCollection and Generic Host/ASP.NET Core style composition.
• Update docs, user guide material, README/docs pattern tables, and the production-readiness catalog.
• Add BenchmarkDotNet coverage comparing fluent and source-generated routes, including overhead and allocation notes.
• Keep solution-wide tests and GitHub checks green.