list_workspaces

List every workspace the current user belongs to.

Returns workspace id, slug, display name, and last activity timestamp for each
workspace, ordered by most recently active first. Does NOT include Creative Units
balance — call `get_workspace` with a workspace_id to get the balance for one
workspace (do not call it for every workspace just to compare balances).

IMPORTANT: Call tool `get_instructions` first for general platform guidance.