Add an in-process post event bus (#13)

Handlers emit PostCreated and PostUpdated after a successful write. Store writes do not publish, and hidden roots are skipped.

Reviewed-on: #13
Co-authored-by: codegirl-007 <s.raide@gmail.com>

internal/events/nop.go

@@ -0,0 +1,9 @@
+package events
+
+import "context"
+
+// Nop is a Publisher used when nothing is subscribed.
+type Nop struct{}
+
+// Publish discards ev.
+func (Nop) Publish(context.Context, any) {}