fix(install): drop stale skills and stamp dream once per repository

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

scripts/install.sh

@@ -23,10 +23,11 @@ if [[ ! -d "${TARGET}" ]]; then
 fi
 
 cd "${REPO_ROOT}"
+src="${REPO_ROOT}/.agents/skills"
+rm -rf "${src}"
 log "skills: restoring from skills-lock.json..."
 npx --yes skills experimental_install
 
-src="${REPO_ROOT}/.agents/skills"
 if [[ ! -d "${src}" ]]; then
 	warn "skills: ${src} not found after install."
 	exit 1