fix(docs): correct per-skill symlink removal snippet in README uninstall

[stedfn]

Closes #1130.

Problem

The manual-uninstall fallback in ## Uninstall → ### Option 2 uses:

find ~/.claude/skills -maxdepth 1 -type l 2>/dev/null | while read -r link; do
  case "$(readlink "$link" 2>/dev/null)" in gstack/*|*/gstack/*) rm -f "$link" ;; esac
done

This finds nothing on real installs. Each ~/.claude/skills/<name>/ is a real directory, and only <name>/SKILL.md inside it is a symlink into gstack/ (per bin/gstack-relink). The find walks one level for symlinks at that depth — there are none — and silently removes nothing.

Fix

Replace with a directory walk that inspects each <name>/SKILL.md:

find ~/.claude/skills -mindepth 1 -maxdepth 1 -type d ! -name gstack 2>/dev/null |
while IFS= read -r dir; do
  link="$dir/SKILL.md"
  [ -L "$link" ] || continue
  target=$(readlink "$link" 2>/dev/null) || continue
  case "$target" in
    gstack/*|*/gstack/*)
      rm -f "$link"
      rmdir "$dir" 2>/dev/null || true
      ;;
  esac
done

• Excludes the top-level gstack/ dir from the walk; step 3 of the same block removes it.
• Uses rm -f + rmdir (vs rm -rf) so any user-added files in a per-skill dir are preserved.
• bin/gstack-uninstall (script mode) already handles the layout correctly via its own walk; only this manual fallback needed updating.

Verification

• bash -n parse-checks clean.
• git diff upstream/main -- README.md shows only the snippet replaced (+12/-3, scoped to the lines under # 2. Remove per-skill symlinks pointing into gstack/).