refactor(types): align manifest types with JSON schema definitions

- Reorganized type hierarchy to mirror schema structure
- Made all properties in ManifestCommunityUrls and ManifestPlatformUrls required (use null for not applicable)
- Fixed type definitions for ManifestModel, ManifestProvider, ManifestCollections
- Added new type guards: isManifestModel, isManifestProvider
- Updated type guard implementations to match schema requirements

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: ericyangpan