Teach agents consolidation and cleanup in the system guide #298

See #290, sections 4 and 5. Do last, once score, weight and bags exist.

Work

• System guide and tool descriptions: when to update instead of adding, when to merge true duplicates (archive the rest with a supersedes link, #214) and when to group related memories into a bag instead.
• Rule: when recall shows a hygiene score below the threshold, clean up the named findings at the end of the session; shared and public changes go through review.
• How to write a bag summary that says what is inside, and a terse summary in general.
• Bump the system guide version.

Acceptance

• Guide text covered by the existing system guide tests; tool description budget test still passes.
• A worked example from this project: one real duplicate merged and one bag created through review.