feat(ui): Add structured observability events

Signed-off-by: Richard Palethorpe <io@richiejp.com>

core/agent/options.go

@@ -53,6 +53,8 @@ type options struct {
 	mcpServers []MCPServer
 
 	newConversationsSubscribers []func(openai.ChatCompletionMessage)
+
+	observer Observer
 }
 
 func (o *options) SeparatedMultimodalModel() bool {
@@ -336,3 +338,10 @@ func WithActions(actions ...types.Action) Option {
 		return nil
 	}
 }
+
+func WithObserver(observer Observer) Option {
+	return func(o *options) error {
+		o.observer = observer
+		return nil
+	}
+}