feat: 补 MIT 许可、自动抓取工具与学科覆盖元数据

登记 chinese-poetry / ck12 / phet，并让 source schema、lint 与 INDEX 能按学科和抓取进度消费。

Co-authored-by: Cursor <cursoragent@cursor.com>

tools/lint_structured.py

@@ -12,7 +12,7 @@
 import sys, os, glob, json
 
 REPO = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
-LICENSES = {"official-free","cc-by","cc-by-sa","cc-nc-education","restricted","internal-only","llm-generated","unknown"}
+LICENSES = {"official-free","mit","cc-by","cc-by-sa","cc-nc-education","restricted","internal-only","llm-generated","unknown"}
 
 def load_source_ids():
     import yaml