list_topics defaults to personal space when space_id omitted; list_spaces explains how to reach it

list_topics now accepts an omitted space_id and resolves it to your personal space automatically (via ensure_personal_space()), so personal-space topics are reachable over MCP without knowing or copying any id. list_spaces now ends with a short note explaining that the personal space is not a shared space and is reached by omitting space_id — so agents and users no longer get stuck when personal topics aren't visible in the spaces list.