Improve search_query MCP tool description for LLM usability

Add a concrete NoteJson example object, a curated inline cheatsheet of
the most useful JsonLogic operators, two additional query examples
(date comparison and multi-condition and), and a pointer to vault_read
as the way to inspect the exact evaluation context for any real file in
the vault.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>