feat: add command mode with :q quit support and tests

Co-authored-by: aider (deepseek/deepseek-coder) <aider@aider.chat>

tui.c

@@ -139,6 +139,61 @@ static void draw_grid(void) {
     refresh();
 }
 
+// Handle command mode input (after pressing ':')
+// Returns true if the application should quit
+static bool handle_command_mode(void) {
+    char cmd_buffer[256];
+    int cmd_pos = 0;
+    memset(cmd_buffer, 0, sizeof(cmd_buffer));
+    
+    // Show command prompt
+    mvprintw(LINES - 1, 0, ":");
+    clrtoeol();
+    refresh();
+    
+    while (1) {
+        int ch = getch();
+        if (ch == ERR) {
+            break;
+        }
+        
+        if (ch == '\n' || ch == '\r') {
+            // Execute command
+            cmd_buffer[cmd_pos] = '\0';
+            
+            // Clear command line
+            mvprintw(LINES - 1, 0, "                ");
+            refresh();
+            
+            // Parse and execute command
+            if (strcmp(cmd_buffer, "q") == 0) {
+                return true;  // Quit
+            }
+            // Add more commands here as needed
+            
+            return false;  // Don't quit
+        } else if (ch == 27) {  // Escape - cancel command mode
+            mvprintw(LINES - 1, 0, "                ");
+            refresh();
+            return false;
+        } else if (ch == KEY_BACKSPACE || ch == 127) {  // Backspace
+            if (cmd_pos > 0) {
+                cmd_pos--;
+                cmd_buffer[cmd_pos] = '\0';
+                mvprintw(LINES - 1, 0, ":%s ", cmd_buffer);
+                refresh();
+            }
+        } else if (cmd_pos < (int)sizeof(cmd_buffer) - 1) {
+            cmd_buffer[cmd_pos++] = (char)ch;
+            cmd_buffer[cmd_pos] = '\0';
+            mvprintw(LINES - 1, 0, ":%s", cmd_buffer);
+            refresh();
+        }
+    }
+    
+    return false;
+}
+
 static void handle_sigint(int sig) {
     (void)sig;
     tui_cleanup();
@@ -252,6 +307,14 @@ void tui_run(Engine *engine) {
                 engine_reset_transport(engine);
                 break;
                 
+            case ':': {
+                bool should_quit = handle_command_mode();
+                if (should_quit) {
+                    return;
+                }
+                break;
+            }
+                
             case '?':
                 show_help = !show_help;
                 break;