Add Liquid template language support for Shopify themes

- Add 'liquid' to Language type and default include patterns
- Create LiquidExtractor with regex-based extraction (tree-sitter-liquid has ABI issues)
- Extract render/include/section references as component nodes
- Extract schema blocks as constant nodes with parsed names
- Extract assign statements as variable nodes
- Create file relationship edges for snippet/section references

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/types.ts

@@ -71,6 +71,7 @@ export type Language =
   | 'ruby'
   | 'swift'
   | 'kotlin'
+  | 'liquid'
   | 'unknown';
 
 // =============================================================================
@@ -496,6 +497,8 @@ export const DEFAULT_CONFIG: CodeGraphConfig = {
     '**/*.php',
     // Ruby
     '**/*.rb',
+    // Liquid (Shopify themes)
+    '**/*.liquid',
   ],
   exclude: [
     // Version control