checkpoint: 重写 langchain agent 前的快照

包含未合入 main 的工作:
- CAS 单点登录接入 (CasSecurityConfig + 4 个 CAS 类)
- LoginController 改 POST + body, 修 URL 密码暴露
- chat_test.py 修 texts→text typo
- 前端外部系统侧边栏 + login API POST
- gateway-nginx.conf

下一步: 从这个分支拉 feat/langgraph-rewrite 做 langchain-chat agent 重写
回滚点: git checkout backup/pre-langgraph

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

chat_web_backend/pom.xml

@@ -191,6 +191,17 @@
             <artifactId>spring-boot-starter-security</artifactId>
         </dependency>
 
+        <!-- CAS 单点登录 -->
+        <dependency>
+            <groupId>org.springframework.security</groupId>
+            <artifactId>spring-security-cas</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.jasig.cas.client</groupId>
+            <artifactId>cas-client-core</artifactId>
+            <version>3.5.0</version>
+        </dependency>
+
         <dependency>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-data-jdbc</artifactId>