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/php.ts

@@ -0,0 +1,63 @@
+import type { Node as SyntaxNode } from 'web-tree-sitter';
+import { getNodeText } from '../tree-sitter-helpers';
+import type { LanguageExtractor } from '../tree-sitter-types';
+
+export const phpExtractor: LanguageExtractor = {
+  functionTypes: ['function_definition'],
+  classTypes: ['class_declaration'],
+  methodTypes: ['method_declaration'],
+  interfaceTypes: ['interface_declaration'],
+  structTypes: [],
+  enumTypes: ['enum_declaration'],
+  typeAliasTypes: [],
+  importTypes: ['namespace_use_declaration'],
+  callTypes: ['function_call_expression', 'member_call_expression', 'scoped_call_expression'],
+  variableTypes: ['property_declaration', 'const_declaration'],
+  nameField: 'name',
+  bodyField: 'body',
+  paramsField: 'parameters',
+  returnField: 'return_type',
+  getVisibility: (node) => {
+    for (let i = 0; i < node.childCount; i++) {
+      const child = node.child(i);
+      if (child?.type === 'visibility_modifier') {
+        const text = child.text;
+        if (text === 'public') return 'public';
+        if (text === 'private') return 'private';
+        if (text === 'protected') return 'protected';
+      }
+    }
+    return 'public'; // PHP defaults to public
+  },
+  isStatic: (node) => {
+    for (let i = 0; i < node.childCount; i++) {
+      const child = node.child(i);
+      if (child?.type === 'static_modifier') return true;
+    }
+    return false;
+  },
+  extractImport: (node, source) => {
+    const importText = source.substring(node.startIndex, node.endIndex).trim();
+
+    // Check for grouped imports: use X\{A, B} - return null for core fallback
+    const namespacePrefix = node.namedChildren.find((c: SyntaxNode) => c.type === 'namespace_name');
+    const useGroup = node.namedChildren.find((c: SyntaxNode) => c.type === 'namespace_use_group');
+    if (namespacePrefix && useGroup) {
+      return null; // Grouped imports create multiple nodes - let core handle
+    }
+
+    // Single import - find namespace_use_clause
+    const useClause = node.namedChildren.find((c: SyntaxNode) => c.type === 'namespace_use_clause');
+    if (useClause) {
+      const qualifiedName = useClause.namedChildren.find((c: SyntaxNode) => c.type === 'qualified_name');
+      if (qualifiedName) {
+        return { moduleName: getNodeText(qualifiedName, source), signature: importText };
+      }
+      const name = useClause.namedChildren.find((c: SyntaxNode) => c.type === 'name');
+      if (name) {
+        return { moduleName: getNodeText(name, source), signature: importText };
+      }
+    }
+    return null;
+  },
+};