Fix store_memory crash (activity_log entity_type constraint)

Storing a memory failed for every client with new row for relation "activity_log" violates check constraint "activity_log_entity_type_chk". The unified-memory RPCs log activity as entity_type='memory', but the activity_log entity_type check constraint was never extended past ('insight','thought') when memories were introduced — so every store_memory/update_memory/delete_memory/move_memory aborted. A new migration extends the constraint to allow 'memory'. ⚠️ Apply manually: supabase db push (or run supabase/migrations/20260609000004_vello_activity_log_allow_memory.sql); CI does not run migrations.