refactor: Extract per-language configs and standalone extractors from tree-sitter.ts

Splits the monolithic tree-sitter.ts (3,358 lines) into modular files:
- 14 language config files under src/extraction/languages/
- 3 standalone extractors (Liquid, Svelte, DFM)
- Shared helpers and types modules to avoid circular imports

Also fixes a bug where Java's extractImport hook incorrectly set
handledRefs: true, preventing unresolved reference creation and
degrading codegraph_explore results for Java codebases.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/extraction/languages/go.ts

@@ -0,0 +1,30 @@
+import { getNodeText, getChildByField } from '../tree-sitter-helpers';
+import type { LanguageExtractor } from '../tree-sitter-types';
+
+export const goExtractor: LanguageExtractor = {
+  functionTypes: ['function_declaration'],
+  classTypes: [], // Go doesn't have classes
+  methodTypes: ['method_declaration'],
+  interfaceTypes: ['interface_type'],
+  structTypes: ['struct_type'],
+  enumTypes: [],
+  typeAliasTypes: ['type_spec'], // Go type declarations
+  importTypes: ['import_declaration'],
+  callTypes: ['call_expression'],
+  variableTypes: ['var_declaration', 'short_var_declaration', 'const_declaration'],
+  methodsAreTopLevel: true,
+  nameField: 'name',
+  bodyField: 'body',
+  paramsField: 'parameters',
+  returnField: 'result',
+  getSignature: (node, source) => {
+    const params = getChildByField(node, 'parameters');
+    const result = getChildByField(node, 'result');
+    if (!params) return undefined;
+    let sig = getNodeText(params, source);
+    if (result) {
+      sig += ' ' + getNodeText(result, source);
+    }
+    return sig;
+  },
+};