The /investigate skill instructed agents to log learnings with type:"investigation",
but bin/gstack-learnings-log:22 rejected anything not in
[pattern, pitfall, preference, architecture, tool, operational]. Every
investigation run exited 1 to stderr and the learning was dropped, silently
to the user.
Fix: add 'investigation' to ALLOWED_TYPES.
Regression test: round-trips a learning with type:"investigation" and asserts
exit 0 + file write; second test reads investigate/SKILL.md.tmpl and asserts
it emits the literal type:"investigation" string, guarding the
template/validator contract at both ends.
Fixes#1423. Reported by diogolealassis.
f94aef7303