feat: add is_terminal_attached syscall

programs/include/montauk/syscall.h

@@ -438,6 +438,11 @@ namespace montauk {
         return syscall1(montauk::abi::SYS_LOG_WRITE, (uint64_t)logMessage);
     }
 
+    // True when stdout is connected to a redirected userspace terminal.
+    inline bool terminal_attached() {
+        return syscall0(montauk::abi::SYS_TERMINAL_ATTACHED) != 0;
+    }
+
     // I/O redirection
     inline int spawn_redir(const char* path, const char* args = nullptr) {
         return (int)syscall2(montauk::abi::SYS_SPAWN_REDIR, (uint64_t)path, (uint64_t)args);