MEMORY.md digest watchdog: surface rules added since 2026-08-10 in August 24 standup

Recurring biweekly MEMORY.md digest. At lease time: (1) inspect MEMORY.md additions/changes since 2026-08-10; (2) extract added rule headings/sections; (3) compose a 3-7 bullet digest; (4) write to memory/digests/2026-08-24-memory-additions.md and inject into the applicable standup body via metadata.body_inserts; (5) complete self and POST the next digest task for +14d.