add update_vocabulary dora input for runtime label changes

The open_vocab engine now accepts an update_vocabulary input event
carrying a UTF-8 comma-separated label string. Labels are re-encoded
immediately via the CLIP text encoder; the next tick uses the new
vocabulary. ZedNative ignores the input via a no-op base class method.

src/main.cc

@@ -95,7 +95,18 @@ int main() {
         }
 
         auto input = event_as_input(std::move(event));
-        (void)input;
+        std::string input_id = std::string(input.id);
+
+        if (input_id == "update_vocabulary") {
+            if (!input.data.empty()) {
+                std::string labels(
+                    reinterpret_cast<const char*>(input.data.data()),
+                    input.data.size());
+                detector->set_labels(labels);
+                std::cout << "Vocabulary updated: " << labels << std::endl;
+            }
+            continue;
+        }
 
         if (!camera.grab()) {
             std::cerr << "Grab failed; attempting to reconnect..." << std::endl;