[#797] vendor bash3boilerplate (MIT) as house standard for new operational scripts

main.sh engine + example.sh demo + adoption policy (new scripts start
from b3bp; existing retrofit opportunistically on touch; vendored copy
pruned from shellcheck scan — upstream code, not house-audited).
Founder directive 2026-09-05.
https://projects.knownelement.com/issues/797

scripts/bash3boilerplate/README.md

@@ -0,0 +1,21 @@
+# bash3boilerplate (b3bp) — house standard for new operational shell scripts
+
+Vendored 2026-09-05 from https://github.com/kvz/bash3boilerplate (MIT,
+attribution headers retained in main.sh/example.sh) per founder directive.
+
+## Adoption policy
+
+- **New operational scripts** in fleet repos should start from
+  `example.sh` (copy, rename, prune) — it gives: strict mode
+  (errexit/errtrace/nounset/pipefail), usage-heredoc-driven CLI parsing,
+  severity-leveled STDERR logging (LOG_LEVEL + NO_COLOR), safe magic
+  variables (`__dir`, `__file`).
+- **Existing scripts**: retrofit opportunistically when touched; do not
+  churn working scripts solely to adopt b3bp.
+- House enforcement (check-rules.sh: shellcheck, secret scan, ticket gate)
+  continues to apply on top — b3bp does not replace it.
+
+## Files
+
+- `main.sh` — the b3bp engine; source it from your script (see example.sh)
+- `example.sh` — full-pattern demonstration