Release v4.91.0

Added

• Specifications accept a description line that says which rule or behavior they witness (#392)
• Modules, features, slices, commands, read models and reactions accept a fenced Markdown documentation block, like events. It is report-only authoring metadata: it never changes the executable model, folder merge keeps the first file's block and reports conflicting blocks, and the MCP declaration-details summary returns description and documentation for every declaration that has them (#392)
• New diagnostics PLAY0558 (malformed documentation block) and PLAY0559 (conflicting module or feature documentation across files) (#392)