SESSION# stats queries lack pagination/time filter -> silent 1MB truncation

Severity: High · Where: stats.ts:65-74,248-255,317-324,383-390,435-442,482-489,534-541,983-990,1052-1059 Every SESSION# query uses begins_with(sk,'SESSION#') with no Limit and no ExclusiveStartKey loop → DynamoDB silently truncates at 1MB → wrong counts on busy sites. Fix: Paginate (see rollups.ts:97-119) or query the existing time-based GSI (Session.ts:229).