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/tree-sitter-helpers.ts

@@ -0,0 +1,80 @@
+/**
+ * Tree-sitter Shared Helpers
+ *
+ * Utility functions used by the core TreeSitterExtractor and per-language extractors.
+ * Extracted to a leaf module to avoid circular imports between tree-sitter.ts and languages/.
+ */
+
+import { Node as SyntaxNode } from 'web-tree-sitter';
+import * as crypto from 'crypto';
+import { NodeKind } from '../types';
+
+/**
+ * Generate a unique node ID
+ *
+ * Uses a 32-character (128-bit) hash to avoid collisions when indexing
+ * large codebases with many files containing similar symbols.
+ */
+export function generateNodeId(
+  filePath: string,
+  kind: NodeKind,
+  name: string,
+  line: number
+): string {
+  const hash = crypto
+    .createHash('sha256')
+    .update(`${filePath}:${kind}:${name}:${line}`)
+    .digest('hex')
+    .substring(0, 32);
+  return `${kind}:${hash}`;
+}
+
+/**
+ * Extract text from a syntax node
+ */
+export function getNodeText(node: SyntaxNode, source: string): string {
+  return source.substring(node.startIndex, node.endIndex);
+}
+
+/**
+ * Find a child node by field name
+ */
+export function getChildByField(node: SyntaxNode, fieldName: string): SyntaxNode | null {
+  return node.childForFieldName(fieldName);
+}
+
+/**
+ * Get the docstring/comment preceding a node
+ */
+export function getPrecedingDocstring(node: SyntaxNode, source: string): string | undefined {
+  let sibling = node.previousNamedSibling;
+  const comments: string[] = [];
+
+  while (sibling) {
+    if (
+      sibling.type === 'comment' ||
+      sibling.type === 'line_comment' ||
+      sibling.type === 'block_comment' ||
+      sibling.type === 'documentation_comment'
+    ) {
+      comments.unshift(getNodeText(sibling, source));
+      sibling = sibling.previousNamedSibling;
+    } else {
+      break;
+    }
+  }
+
+  if (comments.length === 0) return undefined;
+
+  // Clean up comment markers
+  return comments
+    .map((c) =>
+      c
+        .replace(/^\/\*\*?|\*\/$/g, '')
+        .replace(/^\/\/\s?/gm, '')
+        .replace(/^\s*\*\s?/gm, '')
+        .trim()
+    )
+    .join('\n')
+    .trim();
+}