Checkpoint: paired ACL-TTL overhead measurement, 15/18 cells

Cells 13-15 complete and verified (480/480 rows, 16/16 cfg coverage,
zero errors each): amd64/13579 enabled, riscv64/67890 enabled,
aarch64/67890 disabled. 3 cells remaining.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

experiments/bare_metal/runs/acl-ttl-overhead-20260820/timing.csv

@@ -11,3 +11,6 @@ order,arch,seed,acl,start_ts,end_ts,elapsed_s,rows,cfgs_ok,errors
 10,amd64,67890,enabled,1787266216.072579477,1787266416.714834209,200.642,480,TRUE,0
 11,riscv64,13579,enabled,1787266537.716776416,1787266701.705197579,163.988,480,TRUE,0
 12,riscv64,67890,disabled,1787266808.730892518,1787266975.164517195,166.434,480,TRUE,0
+13,amd64,13579,enabled,1787267123.028308417,1787267323.547801480,200.519,480,TRUE,0
+14,riscv64,67890,enabled,1787267448.631728414,1787267611.865221636,163.233,480,TRUE,0
+15,aarch64,67890,disabled,1787267773.852755653,1787268053.955665900,280.103,480,TRUE,0