Memory tools for the agent: query knowledge store, write entries, and use in-process working memory (ContextKeeper).

Uses callbacks on ctx for knowledge store operations:

• ctx.callbacks[:knowledge_search] - (query, opts) -> {:ok, entries} | {:error, term}

• ctx.callbacks[:knowledge_create] - (params) -> {:ok, entry} | {:error, term}

• ctx.callbacks[:knowledge_recent] - (scope_id) -> {:ok, entries} | {:error, term}