feat: validate manifest version during pack command

Add validation to ensure the manifest_version matches the current expected
version (0.2) during the mcpb pack command. This prevents users from
packing extensions with outdated or incorrect manifest versions.

Changes:
- Add CURRENT_MANIFEST_VERSION constant to centralize version management
- Validate manifest version in pack command before creating bundle
- Update init command to use version constant
- Update tests to use version constant
- Fix prettier formatting issues

scripts/build-mcpb-schema.js

@@ -1,4 +1,7 @@
-import { McpbManifestSchema, McpbSignatureInfoSchema } from "../dist/schemas.js";
+import {
+  McpbManifestSchema,
+  McpbSignatureInfoSchema,
+} from "../dist/schemas.js";
 import * as z from "zod/v4";
 import fs from "node:fs/promises";
 import path from "node:path";