tools (volt): the standing carry discharged -- append_only_audit's docstring said "13 cells", its selftest prints 18

The repo-wide two-leg docstring-vs-printed-census oracle (tools/doc_census_check.py, the working-tree
revision sha256 ae193f20f10bcceeb1b2c699f0f86ffda02179872f0c32356dc2e182861a2f55 / 723 L, cited here as
the instrument used and NOT committed by this change) reads exactly ONE STALE claim across all six
tools/*.py scanners at HEAD a82130e:

  STALE tools/append_only_audit.py:41 cells claimed 13 at HEAD -- printed 18 [selftest]

That is the standing carry the control plane returned in reply 05 ("audit docstring says 13 cells not 18")
and carried in the 12:12Z queue tick ("the one carry standing in an owning lane's file"). The tool is
this lane's, so it is discharged here rather than flagged. Change is docstring-only: `13 cells` -> `18
cells` on line 41.

BEFORE tools/append_only_audit.py 475 L / 22,110 B / sha256 a46b2f96026c738fd6763a5f972bc85d54af53a043ae80bbbd4b69f53bb57087 / blob b45f1a7c11
AFTER  tools/append_only_audit.py 475 L / 22,110 B / sha256 81dae4dfecc98bde9b22d8c20ec717d1416248f4603924ac6f84e1d271e65957

Verified: `python3 tools/append_only_audit.py --selftest` -> `selftest: 18 cells, 18 passed, 0 failed`, rc 0.
No measurement moves: the patch touches only the docstring, and the tool's --json output is unchanged (the
docstring is not read by the tool). No item opened or closed; WORK-QUEUE.md untouched.

tools/append_only_audit.py

@@ -38,7 +38,7 @@ is the --json file.
 
 USAGE:
   python3 append_only_audit.py --repo /root/troupe-standup --json out.json
-  python3 append_only_audit.py --selftest          # synthetic repo, 13 cells
+  python3 append_only_audit.py --selftest          # synthetic repo, 18 cells
 """
 import argparse
 import json