Unified detail views, model

CHDataManagement/Model/Post.swift

@@ -65,6 +65,13 @@ final class Post: ObservableObject {
         }
     }
 
+    func isValid(id: String) -> Bool {
+        !id.isEmpty &&
+        content.isValidIdForTagOrPageOrPost(id) &&
+        content.isNewIdForPost(id)
+    }
+
+    @discardableResult
     func update(id newId: String) -> Bool {
         do {
             try content.storage.move(post: id, to: newId)