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/Commands.js

@@ -0,0 +1,15 @@
+export class Commands {
+    static #commands = [];
+
+    static register(command) {
+        this.#commands.push(command);
+    }
+
+    static getAll() {
+        return [...this.#commands];
+    }
+
+    static clear() {
+        this.#commands = [];
+    }
+}