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/CommandOrigin.js

@@ -0,0 +1,20 @@
+import { FeedbackMessageType } from "./FeedbackMessageType";
+
+export class CommandOrigin {
+    constructor(source) {
+        this.source = source;
+    }
+
+    getType() {
+        return this.source.sourceType;
+    }
+
+    getSource() {
+        throw new Error("getSource() not implemented");
+    }
+
+    sendMessage(message) {
+        console.error(`Unknown source type: ${this.source.sourceType}`, message);
+        return FeedbackMessageType.ConsoleError;
+    }
+}