Control: Add monitoring server with ETCP protocol support

- Implement control_server.c/h for monitoring and management
- Add Windows-compatible uasync_poll using select() instead of WSAPoll
- Fix Wintun adapter creation to open existing adapters first
- Add debug category for control server operations
- Update build files to include control server in compilation
- Add test_control_server to test suite

src/control_server.h

@@ -0,0 +1,120 @@
+/*
+ * control_server.h - Control Socket Server for ETCP Monitoring
+ * 
+ * Provides TCP control interface for ETCP connection monitoring
+ */
+
+#ifndef CONTROL_SERVER_H
+#define CONTROL_SERVER_H
+
+#include "../tools/etcpmon/etcpmon_protocol.h"
+#include "../lib/socket_compat.h"
+#include <stdint.h>
+#include <stdio.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Forward declarations */
+struct UTUN_INSTANCE;
+struct UASYNC;
+
+/* Forward declaration */
+struct control_server;
+
+/* Client connection state */
+struct control_client {
+    struct control_client* next;        /* Linked list */
+    struct control_server* server;      /* Back pointer to server */
+    socket_t fd;                        /* Client socket */
+    void* socket_id;                    /* uasync socket ID */
+    
+    /* Receive buffer */
+    uint8_t recv_buffer[ETCPMON_MAX_MSG_SIZE];
+    uint16_t recv_len;                  /* Bytes received so far */
+    
+    /* Selected connection */
+    uint64_t selected_peer_id;          /* 0 = none selected */
+    
+    /* Client state */
+    uint8_t connected;
+};
+
+/* Control server state */
+struct control_server {
+    struct UTUN_INSTANCE* instance;     /* Parent instance */
+    struct UASYNC* ua;                  /* Async context */
+    
+    /* Listening socket */
+    socket_t listen_fd;
+    void* listen_socket_id;             /* uasync socket ID */
+    struct sockaddr_storage bind_addr;  /* Bound address */
+    
+    /* Client connections */
+    struct control_client* clients;     /* Linked list of clients */
+    uint32_t client_count;              /* Number of connected clients */
+    uint32_t max_clients;               /* Maximum allowed clients */
+    
+    /* Log file */
+    FILE* log_file;
+};
+
+/* ============================================================================
+ * Public API
+ * ============================================================================ */
+
+/* Initialize control server
+ * 
+ * Creates listening socket and registers with uasync
+ * 
+ * Parameters:
+ *   server  - Server state structure to initialize
+ *   ua      - uasync context for event handling
+ *   instance - Parent utun instance
+ *   bind_addr - Address to bind (from config control_sock)
+ *   max_clients - Maximum concurrent client connections
+ * 
+ * Returns:
+ *   0 on success, -1 on error
+ */
+int control_server_init(struct control_server* server,
+                        struct UASYNC* ua,
+                        struct UTUN_INSTANCE* instance,
+                        struct sockaddr_storage* bind_addr,
+                        uint32_t max_clients);
+
+/* Shutdown control server
+ * 
+ * Closes all client connections and listening socket
+ * 
+ * Parameters:
+ *   server - Server state to shutdown
+ */
+void control_server_shutdown(struct control_server* server);
+
+/* Process periodic updates
+ * 
+ * Should be called periodically (e.g., from main loop) to send
+ * metrics updates to clients that have selected connections
+ * 
+ * Parameters:
+ *   server - Server state
+ */
+void control_server_process_updates(struct control_server* server);
+
+/* Get number of connected clients
+ * 
+ * Parameters:
+ *   server - Server state
+ * 
+ * Returns:
+ *   Number of connected clients
+ */
+uint32_t control_server_get_client_count(const struct control_server* server);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* CONTROL_SERVER_H */