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packing extensions with outdated or incorrect manifest versions.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

README.md

@@ -1,8 +1,9 @@
 # MCP Bundles (MCPB)
 
 > **⚠️ IMPORTANT NOTICE: This project is being renamed from DXT (Desktop Extensions) to MCPB (MCP Bundles)**
-> 
+>
 > If you're looking for the DXT tools, they have been renamed to MCPB. Please update your dependencies and tooling:
+>
 > - `dxt` CLI is now `mcpb`
 > - `.dxt` files are now `.mcpb` files
 > - `@anthropic-ai/dxt` package will be moved to `@anthropic-ai/mcpb`
@@ -154,4 +155,4 @@ npm test
 
 # License
 
-This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details.
+This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details.