v5.2.0 - context_delete + Now item rename

Added

• Delete context entries via MCP. New context_delete MCP tool removes a
  single context entry (action plus its content, metadata and relations) by ID.
  The delete capability already existed in the backend (delete_entry) and CLI
  (cm delete); only the MCP surface was missing, leaving context entries the
  odd entity out next to notes, now-items and infra, which all expose delete.
  The tool is deliberately ID-only - there is no delete-by-query - to prevent a
  single call from wiping many entries. Context entries remain non-editable in
  place by design: to correct a wrong entry, delete it and context_save a
  corrected one, which keeps the entry log a record of what was actually saved
  rather than a silently-rewritten surface. (No context_edit is provided.)
• Rename Now items in place. New cm now edit <id> <title> subcommand and
  now_edit MCP tool. Previously a title could only be changed by deleting the
  item and re-adding it, which silently reset its position, creation time and
  linked-entity reference. Editing is title-only by design (bucket changes go
  through move, status through done/remove) and reuses the same title
  validation as add, so the single-line 200-character limit is enforced the
  same way on both paths.