feat(bench): add --since filter to analyze; journal session

analysis/client-perf/harness/analyze.py

@@ -176,8 +176,11 @@ def main(argv=None):
     ap.add_argument("--noise", help="label whose spread is the win threshold, e.g. B0")
     ap.add_argument("--include-invalid", action="store_true")
     ap.add_argument("--exclude-backup", action="store_true")
+    ap.add_argument("--since", help="only rows with ts >= this ISO time, e.g. 2026-10-16T22:24")
     a = ap.parse_args(argv)
     rows = load_rows(a.file)
+    if a.since:
+        rows = [r for r in rows if r.get("ts", "") >= a.since]
     total = len(rows)
     if not a.include_invalid:
         rows = [r for r in rows if is_valid(r, a.exclude_backup)]