docs(build): correct the citation receipt line count (#1816)

agents/gladstone/work/hostcheck-item5/BUILD.md

@@ -249,3 +249,5 @@ Morgana-0213 found the fixture/F6 deltas CLEAN statically. No Node/tests run;
 Morgana's eventual run waits for Sage's row and CLEAR after the 220+216 landing.
 Numstat for this follow-up: host-run-sheet.md +1/-1; BUILD.md +9/-0.
 Static receipt: git diff --check passed.
+
+Correction: 0f3d874d4 added 10 BUILD.md lines, not 9; the git numstat is authoritative.