Reduce false action_required outcomes in closed-PR automation and Sighthound scan workflows

[Copilot]

Three workflows were intermittently/consistently ending in action_required because expected execution paths were gated off (copilot/* branch exclusions and conditional agent execution). This PR removes those blockers so intended post-close/update/triage logic can run deterministically.

• Closed PR labeling: remove branch-based skip

  • Updated label-closed-prs.yml to stop excluding copilot/* branches.
  • Result: unmerged closed PRs are labeled regardless of author branch prefix.

• PR description updater: allow Copilot-authored merged PRs

  • Updated pr-description-caveman.md to remove the copilot/* exclusion from the top-level merged-PR condition.
  • Recompiled lockfile to keep runtime YAML in sync.

• Sighthound scan: always run triage stage

  • Updated sighthound-security-scan.md to remove the top-level if that only ran the agent when actionable findings were pre-detected.
  • Flow now allows the agent to emit noop on empty actionable sets instead of skipping the stage and surfacing action_required.
  • Recompiled lockfile to reflect the frontmatter/control-flow change.

# before
if: needs.sighthound_scan.outputs.actionable_findings_detected == 'true'

# after
# (condition removed at workflow top level; agent job decides noop vs issue)