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

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

skills/dream/SKILL.md

@@ -120,7 +120,7 @@ for the operator corrections the window revealed. Both keep their own
 confirmation steps; the dream never writes a skill on their behalf.
 
 Close the run by refreshing this repository's reminder stamp, so the next hint
-is twelve hours out: `date +%s > "$(git rev-parse --absolute-git-dir)/.dream-stamp"`.
+is twelve hours out: `date +%s > "$(git rev-parse --path-format=absolute --git-common-dir)/.dream-stamp"`.
 
 ## Rules
 

skills/dream/hooks/reminder.sh

@@ -10,7 +10,7 @@ interval="${DREAM_INTERVAL_SECONDS:-43200}"
 if [[ -n "${DREAM_STAMP:-}" ]]; then
 	stamp="${DREAM_STAMP}"
 else
-	git_dir="$(git rev-parse --absolute-git-dir 2>/dev/null)" || exit 0
+	git_dir="$(git rev-parse --path-format=absolute --git-common-dir 2>/dev/null)" || exit 0
 	stamp="${git_dir}/.dream-stamp"
 fi