Onboarding: confirm before storing a Memory into a shared Space (privacy trust)

When an AI agent captures a Memory through memsprout's MCP tools, it will now only file it into a shared Space when you've named that Space by name in the conversation — otherwise it always lands safely in your personal space, never a team Space by inference or guess. Whenever a Memory does land in a shared Space, the response names the Space and how many people can see it, so a shared write is always visible, never silent.