fix: AGENTIC licence line + a2ml-validate-action repin (#145)

Ruleset refused a direct push, so this lands by PR. Two mechanical
fixes, owner-ruled:

1. **AGENTIC licence line** — `Never use AGPL license (…)` contradicts
`LICENCE-POLICY.adoc` Rules 3/4/5 (which mandate AGPL for their scopes).
Replaced with the policy pointer used in `rsr-template-repo#45`. See
`standards#646`.
2. **`a2ml-validate-action` repin** — the previously-pinned SHAs never
existed; the repo was only created 2026-08-28 (split from
`a2ml/actions/validate`, history preserved). Repinned to its real HEAD.
See `standards#669`.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: hyperpolymath

.machine_readable/descriptiles/AGENTIC.a2ml

@@ -23,7 +23,12 @@ can-create-files = true
 # - Never commit secrets or credentials
 # - Never use banned languages: TypeScript, Python (except SaltStack), Go, Node.js, Bun, npm
 # - Never place checkpoint files outside .machine_readable/
-# - Never use AGPL-3.0 license (use MPL-2.0)
+# - Never relicense an existing file, and never run an automated licence
+#   sweep (LICENCE-POLICY.adoc A2). New files get correct SPDX from birth.
+# - Never assume a licence. Read standards/LICENCE-POLICY.adoc: Rule 1
+#   defaults to MPL-2.0 (code) / CC-BY-SA-4.0 (prose), but Rule 3
+#   (co-developed), Rule 4 (network-deployed services) and Rule 5
+#   (games) are AGPL-3.0-or-later, and Rule 2 names the PMPL register.
 # - Full six-prover run (proofs/verify-all-provers.sh) needs Mathlib/Isabelle/Mizar
 #   installed; the lighter provers (Coq/Agda/Z3/Idris) run cheaply