fix: anchor .claude skill un-ignore to repo root

Previous rules un-ignored nested .claude/ dirs (e.g. md/<topic>/.claude/
harness state). Leading-slash anchoring scopes the exception to the repo
root skill only.

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

.gitignore

@@ -4,12 +4,15 @@ pdfs/
 # Generated OCR worklist (regenerated each run)
 needs-ocr.txt
 
-# Claude Code session/harness state (but version committed skills)
+# Claude Code session/harness state — ignored everywhere (incl. nested .claude/)
-.claude/*
+.claude/
-!.claude/skills/
+# ...except the committed research skill at the REPO ROOT only (leading slash)
-.claude/skills/*
+!/.claude/
-!.claude/skills/research/
+/.claude/*
-!.claude/skills/research/**
+!/.claude/skills/
+/.claude/skills/*
+!/.claude/skills/research/
+!/.claude/skills/research/**
 
 # Python
 .venv/