feat: add :nick command and /me action messages

- :nick/:name <name>: change username in-session with full validation,
  thread-safe update under write lock, and system broadcast
- /me <action>: IRC-style action messages displayed as "* user action"
- Updated help text (EN/ZH) and manpage with new commands

Closes #38

src/ssh_server.c

@@ -1147,6 +1147,7 @@ static void execute_command(client_t *client) {
                        "        Available Commands\n"
                        "========================================\n"
                        "list, users, who    - Show online users\n"
+                       "nick/name <name>    - Change nickname\n"
                        "msg/w <user> <text> - Whisper to user\n"
                        "help, commands      - Show this help\n"
                        "clear, cls          - Clear command output\n"
@@ -1201,6 +1202,40 @@ static void execute_command(client_t *client) {
             }
         }
 
+    } else if (strncmp(cmd, "nick ", 5) == 0 || strncmp(cmd, "name ", 5) == 0) {
+        char *new_name = cmd + 5;
+        while (*new_name == ' ') new_name++;
+
+        if (new_name[0] == '\0') {
+            buffer_appendf(output, sizeof(output), &pos,
+                           "Usage: nick <new_username>\n");
+        } else if (!is_valid_username(new_name)) {
+            buffer_appendf(output, sizeof(output), &pos,
+                           "Invalid username\n");
+        } else {
+            char validated_name[MAX_USERNAME_LEN];
+            snprintf(validated_name, sizeof(validated_name), "%s", new_name);
+            if (utf8_strlen(validated_name) > 20) {
+                utf8_truncate(validated_name, 20);
+            }
+
+            char old_name[MAX_USERNAME_LEN];
+            pthread_rwlock_wrlock(&g_room->lock);
+            snprintf(old_name, sizeof(old_name), "%s", client->username);
+            snprintf(client->username, MAX_USERNAME_LEN, "%s", validated_name);
+            pthread_rwlock_unlock(&g_room->lock);
+
+            message_t nick_msg = { .timestamp = time(NULL) };
+            snprintf(nick_msg.username, MAX_USERNAME_LEN, "系统");
+            snprintf(nick_msg.content, MAX_MESSAGE_LEN,
+                     "%s 更名为 %s", old_name, client->username);
+            room_broadcast(g_room, &nick_msg);
+            message_save(&nick_msg);
+
+            buffer_appendf(output, sizeof(output), &pos,
+                           "Nickname changed: %s -> %s\n", old_name, client->username);
+        }
+
     } else if (strcmp(cmd, "q") == 0 || strcmp(cmd, "quit") == 0 ||
                strcmp(cmd, "exit") == 0) {
         client->connected = false;
@@ -1296,8 +1331,18 @@ static bool handle_key(client_t *client, unsigned char key, char *input) {
                     message_t msg = {
                         .timestamp = time(NULL),
                     };
+                    if (strncmp(input, "/me ", 4) == 0 && input[4] != '\0') {
+                        msg.username[0] = '*';
+                        msg.username[1] = '\0';
+                        int n = snprintf(msg.content, sizeof(msg.content), "%s %s",
+                                         client->username, input + 4);
+                        if (n >= (int)sizeof(msg.content)) {
+                            msg.content[sizeof(msg.content) - 1] = '\0';
+                        }
+                    } else {
                         snprintf(msg.username, sizeof(msg.username), "%s", client->username);
                         snprintf(msg.content, sizeof(msg.content), "%s", input);
+                    }
                     room_broadcast(g_room, &msg);
                     message_save(&msg);
                     input[0] = '\0';

src/tui.c

@@ -301,6 +301,8 @@ const char* tui_get_help_text(help_lang_t lang) {
                "\n"
                "AVAILABLE COMMANDS:\n"
                "  list, users, who  - Show online users\n"
+               "  nick/name <name>  - Change nickname\n"
+               "  msg/w <user> <text> - Whisper to user\n"
                "  help, commands    - Show available commands\n"
                "  clear, cls        - Clear command output\n"
                "\n"
@@ -347,6 +349,8 @@ const char* tui_get_help_text(help_lang_t lang) {
                "\n"
                "可用命令:\n"
                "  list, users, who  - 显示在线用户\n"
+               "  nick/name <名字>  - 更改昵称\n"
+               "  msg/w <用户> <文本> - 私聊\n"
                "  help, commands    - 显示可用命令\n"
                "  clear, cls        - 清空命令输出\n"
                "\n"

tnt.1

@@ -97,6 +97,8 @@ Ctrl+C	Disconnect
 .TS
 l l.
 :list	Show online users
+:nick \fIname\fR	Change nickname
+:name \fIname\fR	Alias for :nick
 :msg \fIuser text\fR	Send private whisper
 :w \fIuser text\fR	Short alias for :msg
 :help	Show available commands