Fixes#114 and #122 by adding --description/-d flag to bd update CLI
and description parameter to MCP update_issue tool.
Changes:
- CLI: Added --description flag to updateCmd
- RPC: Added Description field to UpdateArgs
- Daemon: Updated updatesFromArgs to handle description
- MCP: Added description to update_issue, UpdateIssueParams, and clients
- Storage: description already supported in allowedUpdateFields
Tested in both daemon and direct modes.