feat: Server Mode with WebSocket direct connect (Phase 3A)

- DirectConnectServer: lifecycle management, auth token, port config
- DirectConnectWebSocketHandler: WebSocket handler with session management
- ServerSession: per-connection AgentLoop with permission forwarding
- ServerMessage: 7-type JSON protocol (user/assistant/result/control/interrupt/keep_alive/error)
- ServerModeAutoConfiguration: conditional Spring config with @EnableWebSocket
- WebSocketServerConfig: endpoint registration and container settings
- ClaudeCodeApplication: --server flag detection, web-application-type override
- ClaudeCodeRunner: skip TUI in server mode, block on shutdown signal
- pom.xml: added spring-boot-starter-websocket dependency

Server mode: --server [--server-port=12321] [--server-token=xxx]
Env vars: CLAUDE_CODE_SERVER_MODE, CLAUDE_CODE_SERVER_PORT, CLAUDE_CODE_SERVER_TOKEN

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

pom.xml

@@ -44,6 +44,12 @@
             <artifactId>spring-boot-starter-web</artifactId>
         </dependency>
 
+        <!-- Spring Boot WebSocket（Server Mode 使用） -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-websocket</artifactId>
+        </dependency>
+
         <!-- Spring AI Anthropic（Claude 模型调用） -->
         <dependency>
             <groupId>org.springframework.ai</groupId>