Adds an experimental endpoint and backend query to list sessions across all projects/directories, with filters (directory/roots/search/start), archived inclusion toggle, and cursor-based pagination via an x-next-cursor header, plus tests to verify behavior. This enables clients to build a unified “recent activity” view without recursively scanning directories and includes project metadata alongside each session. Concerns: it’s an experimental route but could still be performance-sensitive (global DB scan, LIKE search, large limits) and the cursor uses time_updated which may be non-unique/edge-prone without careful tie-breaking across pages.