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packing extensions with outdated or incorrect manifest versions.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
This section was added alongside the rename but is not necessary for the dxt -> mcpb rename itself. Removing to keep the rename commit focused on just the naming changes.
