Context Mode Purge

Permanently deletes session data for this project. Two scopes are supported (issue #520):

• Project scope (scope: "project"): wipes EVERYTHING — knowledge base, all session DB rows for every session, events markdown, and stats.
• Session scope (sessionId: "<id>" or scope: "session"): wipes ONLY the matching session's rows + FTS5 chunks. Sibling sessions, project stats, and the FTS5 store file are preserved.

Instructions