Feature Request: Add Kotlin lang support

I'm using Lat in a Kotlin Multiplatform project and would love to have Kotlin source references supported.

Currently, file-level links work, but it's not possible to reference Kotlin classes, functions, or properties directly.

It would be great to support .kt and .kts files, including:

• Classes, interfaces, objects, and their members
• Top-level functions and properties
• Extension functions
• expect/actual declarations
• // @lat: backlinks, including in tests

For example, something like [[shared/src/commonMain/kotlin/MessageRepository.kt#MessageRepository#saveMessage]] should resolve and be validated by lat check.

I'm happy to work on a PR for this. Would be good to hear if there's a preferred approach to adding support for a new language.