Kotlin target (`Metano.Compiler.Kotlin`)

[danfma]

Priority: Future

Background: Same as #TBD (Dart target). ADR-0001 establishes the per-target project pattern.

Goal

A new `Metano.Compiler.Kotlin` project that transpiles annotated C# types into idiomatic Kotlin, targeted at native Android consumers (or any JVM Kotlin project that wants to share domain types with a .NET backend).

Scope (high level)

• New project `src/Metano.Compiler.Kotlin/` implementing `ITranspilerTarget`
• Kotlin-specific AST + Printer
• CLI tool: `metano-kotlin`
• Lowering rules:
  • C# records → Kotlin `data class` (native `==` / `hashCode` / `copy`)
  • C# sealed hierarchies → Kotlin `sealed class` (tight fit)
  • C# enums → Kotlin `enum class`
  • Nullable types → Kotlin `T?`
  • Async / await → Kotlin coroutines (`suspend` / `Flow`)
• BCL mappings: `DateTime` → `kotlinx.datetime.LocalDateTime`, `decimal` → `java.math.BigDecimal`, `Guid` → `java.util.UUID`
• LINQ → Kotlin's `Sequence` operators (very close semantic match)
• Gradle integration story — how does a Kotlin consumer pull in the generated sources?
• `[EmitPackage]` support for Maven / Gradle coordinates
• Sample project `samples/SampleTodo.Kotlin/`

Notes

Kotlin is an excellent target for Metano — the type systems line up tightly (nullable, data classes, sealed hierarchies, generics with variance). Lower porting friction than Dart.

Part of #14.

[danfma]

Spec mapping: Spec change request — new target. Same as #28 (Dart). Would need Kotlin-specific FRs. Core architecture (ADR-0001) is ready.