feat(extraction): read headless mode from config instead of hardcoding

Add headless field to extraction config schema (default: true).
Extractor handler now reads globalConfig.extraction.headless instead
of hardcoding true. Users can set headless: false in config.yaml
to show the browser window during extraction for debugging.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/main/services/config/config-manager.ts

@@ -78,7 +78,8 @@ const DEFAULT_CONFIG: FullConfig = {
     verbose: true,
     autoConvert: true,
     mergeBatches: true,
-    enableDbPersistence: true
+    enableDbPersistence: true,
+    headless: true
   },
   validation: {
     dataSource: 'database_full',