## 1. Implementation
- [ ] 1.1 Add `ckan_tag_list` tool handler that calls CKAN faceting and returns tag counts
- [ ] 1.2 Register the tool in the MCP server tool index
- [ ] 1.3 Add markdown and JSON response formatting
- [ ] 1.4 Add input validation for `server_url`, `q`, `fq`, `tag_query`, and `limit`
- [ ] 1.5 Add/update tests for tag listing and filtering
- [ ] 1.6 Update README/examples to include tag discovery usage
