feat(cli): add Command pipeline base classes

The Command base class, Commands registry, FeedbackMessageType enum,
and four CommandOrigin subclasses (Player/Entity/Block/Server) that
every CLI command in this branch depends on. Without these files the
new commands fail to resolve imports at module load.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

packs/BP/scripts/classes/Commands/EntityCommandOrigin.js

@@ -0,0 +1,13 @@
+import { CommandOrigin } from "./CommandOrigin";
+import { FeedbackMessageType } from "./FeedbackMessageType";
+
+export class EntityCommandOrigin extends CommandOrigin {
+    getSource() {
+        return this.source.sourceEntity;
+    }
+
+    sendMessage(message) {
+        this.getSource().sendMessage(message);
+        return FeedbackMessageType.ChatMessage;
+    }
+}