Move review actions into the platform, emit events on change

Still not seeing updates in the sidebar, however.

platform/error.go

@@ -0,0 +1,14 @@
+package platform
+
+import (
+	"fmt"
+)
+
+type ErrorNotFound struct {
+	message string
+}
+
+func (e ErrorNotFound) Error() string { return fmt.Sprintf("not found: %s", e.message) }
+func newNotFound(format string, m ...any) error {
+	return &ErrorNotFound{message: fmt.Sprintf(format, m...)}
+}