P1 (part 1): move skilltools core -> tool/ (clean, verbatim)

The tool registry core (registry, permission model, Invocation, gated-tool
wrapper, ssrf guard, hmac, encryption, argcoerce, helpers, rootrun,
session_tools, webhook_rate_limit) had zero mort coupling — it imports only
majordomo/llm + x/crypto/hkdf — so it moves verbatim with a package rename
(skilltools -> tool). All same-package tests came along and pass; the SSRF,
gated-wrapper, encryption and output-pattern invariants are re-anchored here.

majordomo re-enters the module graph (now pinned to the latest, incl. the
front-loaded-output fix). model/ + llmmeta + structured follow next.

Docs: CLAUDE.md now requires README/examples to stay in sync with changes in
the same commit; CI skips docs/example-only pushes via paths-ignore.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

go.mod

@@ -1,3 +1,8 @@
 module gitea.stevedudenhoeffer.com/steve/executus
 
 go 1.26.2
+
+require (
+	gitea.stevedudenhoeffer.com/steve/majordomo v0.0.0-20260626223738-1fd7109a42f3
+	golang.org/x/crypto v0.53.0
+)