Add interface dispatch fixtures and METHOD_IMPLEMENTS edge assertions for
the 4 remaining languages that support interfaces:
- C#: IRepository interface with Find/Save, SqlRepository implements
- TypeScript: IRepository interface with find/save, SqlRepository implements
- Kotlin: Repository interface with find/save, SqlRepository implements
- Dart: abstract Repository with find/save, SqlRepository implements
Fix: Kotlin interfaces use class_declaration AST node type — added
keyword-based detection in findEnclosingClassInfo to correctly label
them as Interface (not Class), enabling METHOD_IMPLEMENTS edge emission.
Total METHOD_IMPLEMENTS integration coverage: 9 languages
(Java, PHP, Rust, Swift, Python, C#, TypeScript, Kotlin, Dart)
