engine: timeline panel leftover commands migrate to the facade (round 3)

- new primitives: clip_toggle_enabled (per-block flip), clip_set_linked,
  sequence_add_default_transition (config-driven, sequence timebase),
  node_set_label_many, node_set_color_label, plus observation getters
- toggle-links, default transitions, enable toggles, color labels, and
  block renaming now go through the facade; the stray empty undo entry
  from block renaming is gone along the way
- nest/multicam/waveform-sync stay as documented composites: they mix
  redo_now intermediate state, graph surgery, and app-side computation
  that a single primitive cannot express faithfully
- the timeline panel's command execution paths are now fully migrated

engine/src/capi/node.cpp

@@ -549,6 +549,66 @@ int oakengine_node_set_label_ex(OakEngineNode *self, const char *label,
 	return OAKENGINE_OK;
 }
 
+int oakengine_node_set_label_many(OakEngineNode **nodes, int count,
+								  const char *label)
+{
+	set_error(QString());
+	if (count < 0 || (count > 0 && !nodes)) {
+		set_error(QStringLiteral("invalid arguments"));
+		return OAKENGINE_E_INVALID;
+	}
+	if (count == 0) {
+		return OAKENGINE_OK;
+	}
+	// One multi-node rename command, like Core::label_nodes().
+	auto *command = new olive::NodeRenameCommand();
+	const QString text = QString::fromUtf8(label ? label : "");
+	for (int i = 0; i < count; i++) {
+		if (!nodes[i]) {
+			set_error(QStringLiteral("invalid node at index %1").arg(i));
+			delete command;
+			return OAKENGINE_E_INVALID;
+		}
+		command->add_node(impl(nodes[i]), text);
+	}
+	push_or_run(command, QStringLiteral("Rename Nodes"));
+	return OAKENGINE_OK;
+}
+
+int oakengine_node_set_color_label(OakEngineNode **nodes, int count,
+								   int color_index)
+{
+	set_error(QString());
+	if (count < 0 || (count > 0 && !nodes)) {
+		set_error(QStringLiteral("invalid arguments"));
+		return OAKENGINE_E_INVALID;
+	}
+	if (count == 0) {
+		return OAKENGINE_OK;
+	}
+	olive::MultiUndoCommand *command = new olive::MultiUndoCommand();
+	for (int i = 0; i < count; i++) {
+		if (!nodes[i]) {
+			set_error(QStringLiteral("invalid node at index %1").arg(i));
+			delete command;
+			return OAKENGINE_E_INVALID;
+		}
+		command->add_child(
+			new olive::NodeOverrideColorCommand(impl(nodes[i]),
+												color_index));
+	}
+	push_or_run(command, QStringLiteral("Set Node Color Labels"));
+	return OAKENGINE_OK;
+}
+
+int oakengine_node_get_color_label(const OakEngineNode *self)
+{
+	if (!self) {
+		return -1;
+	}
+	return impl(self)->get_override_color();
+}
+
 int oakengine_node_input_count(const OakEngineNode *self)
 {
 	return self ? impl(self)->inputs().size() : 0;