docs(link-skills): mark as a dev-only script

Add a header note clarifying that link-skills.sh is a dev-only script for
maintainers, not a supported installer, and that modifications or requests
for modification will not be approved.

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

scripts/link-skills.sh

@@ -1,6 +1,10 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
+# NOTE: This is a dev-only script, intended for use by maintainers of this repo.
+# It is not a supported installer. Modifications to it — or requests for
+# modifications — will not be approved.
+#
 # Links all skills in the repository into the local skill directories used by
 # each agent harness:
 #   - ~/.claude/skills  — Claude Code