feat: Fix Go struct/interface extraction by refactoring type_spec handling through type alias resolver

Addresses Go's tree-sitter parsing where structs and interfaces are wrapped in type_spec nodes rather than appearing as direct node types. Moves struct_type and interface_type detection from direct node type matching to a new resolveTypeAliasKind resolver that examines the inner type field, ensuring proper extraction with field visiting and inheritance detection.

src/extraction/languages/go.ts

@@ -5,8 +5,8 @@ export const goExtractor: LanguageExtractor = {
   functionTypes: ['function_declaration'],
   classTypes: [], // Go doesn't have classes
   methodTypes: ['method_declaration'],
-  interfaceTypes: ['interface_type'],
-  structTypes: ['struct_type'],
+  interfaceTypes: [],  // Handled via type_spec → resolveTypeAliasKind
+  structTypes: [],     // Handled via type_spec → resolveTypeAliasKind
   enumTypes: [],
   typeAliasTypes: ['type_spec'], // Go type declarations
   importTypes: ['import_declaration'],
@@ -27,6 +27,15 @@ export const goExtractor: LanguageExtractor = {
     }
     return sig;
   },
+  resolveTypeAliasKind: (node, _source) => {
+    // Go type_spec: `type Foo struct { ... }` or `type Bar interface { ... }`
+    // The inner type is in the 'type' field of the type_spec node
+    const typeChild = getChildByField(node, 'type');
+    if (!typeChild) return undefined;
+    if (typeChild.type === 'struct_type') return 'struct';
+    if (typeChild.type === 'interface_type') return 'interface';
+    return undefined;
+  },
   getReceiverType: (node, source) => {
     // Go method_declaration has a "receiver" field: func (sl *scrapeLoop) run(...)
     // The receiver is a parameter_list containing a parameter_declaration