chore: 完善 .gitignore — 排除 sqlite3/Thumbs.db/大文件文档

.gitignore

@@ -4,6 +4,7 @@ __pycache__/
 venv/
 *.db
 .env
+*.sqlite3
 
 # Frontend
 node_modules/
@@ -11,7 +12,11 @@ dist/
 
 # OS
 .DS_Store
+Thumbs.db
 
 # Runtime
 .pids/
 logs/
+
+# Docs (large/generated)
+OPTIMIZATION_GUIDE*.md