[Discovery] mcp/dockerhub - Docker Hub API Integration

## Project Association

This issue tracks the `mcp/dockerhub` MCP server in the core profile.

### Server Details
- **Name**: dockerhub
- **Source**: https://github.com/docker/hub-mcp
- **Docker Hub**: https://hub.docker.com/r/mcp/dockerhub
- **Category**: docker
- **Language**: TypeScript/Node.js

### Transport Status
- **Current**: Native HTTP support (`--transport=http`)
- **Implementation**: No wrapper needed
- **Docker Image**: `mcp/dockerhub` (official)

### Tools Provided
- `search`: Search Docker Hub for images
- `listRepositoriesByNamespace`: List repositories in a namespace
- `createRepository`: Create a new repository
- `getRepositoryInfo`: Get repository information
- `updateRepositoryInfo`: Update repository details
- `checkRepository`: Check if a repository exists
- `listRepositoryTags`: List available tags for a repository
- `getRepositoryTag`: Get details about a specific tag
- `checkRepositoryTag`: Check if a tag exists
- `listNamespaces`: List available namespaces
- `getPersonalNamespace`: Get personal namespace info
- `listAllNamespacesMemberOf`: List namespaces user is member of
- `dockerHardenedImages`: Get Docker hardened images info

### Docker Status
- Official image: `mcp/dockerhub`
- No custom build needed
- HADOLint: N/A (official image)

### Notes
- Requires `HUB_PAT_TOKEN` environment variable
- Native HTTP transport on port 3000
- Well-maintained by Docker team

### Tracking
- [ ] Document all tools comprehensively
- [ ] Test all API endpoints
- [ ] Consider Rust rewrite for performance