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>

config.template.yaml

@@ -40,6 +40,7 @@ extraction:
   autoConvert: true
   mergeBatches: true
   enableDbPersistence: true
+  headless: true # 浏览器无头模式，true=后台运行，false=显示浏览器窗口（调试用）
 
 validation:
   dataSource: database_full