feat: Add TypeScript abstract class extraction and fix arrow function naming

Addresses TypeScript abstract classes missing by adding abstract_class_declaration to classTypes. Fixes single-expression arrow functions being silently dropped by preventing extractName from searching identifiers in arrow_function/function_expression bodies, ensuring they return  for proper parent name resolution instead of incorrectly using body identifiers.

src/extraction/languages/typescript.ts

@@ -3,7 +3,7 @@ import type { LanguageExtractor } from '../tree-sitter-types';
 
 export const typescriptExtractor: LanguageExtractor = {
   functionTypes: ['function_declaration', 'arrow_function', 'function_expression'],
-  classTypes: ['class_declaration'],
+  classTypes: ['class_declaration', 'abstract_class_declaration'],
   methodTypes: ['method_definition', 'public_field_definition'],
   interfaceTypes: ['interface_declaration'],
   structTypes: [],

src/extraction/tree-sitter.ts

@@ -70,6 +70,14 @@ function extractName(node: SyntaxNode, source: string, extractor: LanguageExtrac
     }
   }
 
+  // Arrow/function expressions get their name from the parent variable_declarator,
+  // not from identifiers in their body. Without this, single-expression arrow
+  // functions like `const fn = () => someIdentifier` get named "someIdentifier"
+  // instead of "fn", because the fallback below finds the body identifier.
+  if (node.type === 'arrow_function' || node.type === 'function_expression') {
+    return '<anonymous>';
+  }
+
   // Fall back to first identifier child
   for (let i = 0; i < node.namedChildCount; i++) {
     const child = node.namedChild(i);