feat: Add complete Kotlin language support with fun interface handling

Addresses Kotlin interfaces/enums extracted as classes, zero function calls, and missing `fun interface` declarations. Adds classifyClassNode to distinguish interfaces/enums from classes, resolveBody hook for non-field grammar, navigation_expression call handling, getReceiverType for extension functions, and visitNode hook to detect `fun interface` misparse patterns from tree-sitter-kotlin's lack of Kotlin 1.4+ syntax support. Verified against Koin and LeakCanary codebases.

src/extraction/tree-sitter-types.ts

@@ -154,7 +154,7 @@ export interface LanguageExtractor {
    * Classify a class_declaration node when the grammar reuses one node type
    * for multiple concepts (e.g. Swift uses class_declaration for classes, structs, and enums).
    */
-  classifyClassNode?: (node: SyntaxNode) => 'class' | 'struct' | 'enum';
+  classifyClassNode?: (node: SyntaxNode) => 'class' | 'struct' | 'enum' | 'interface';
 
   /**
    * Resolve the body node for a function/method/class when it's not a child field.