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

Closes #1130.

The manual-uninstall fallback in `## Uninstall` → `### Option 2` used
`find ~/.claude/skills -maxdepth 1 -type l`, which 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/`. The find never
matched, so the snippet silently removed nothing.

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

  find ~/.claude/skills -mindepth 1 -maxdepth 1 -type d ! -name gstack
  → check $dir/SKILL.md is a symlink → readlink it
  → if target is gstack/* or */gstack/*: rm -f the link, rmdir the dir
    (only if empty — preserves any user-added files)

Excludes the top-level `gstack/` dir from the walk; that's removed by
step 3 of the same uninstall block.

`bin/gstack-uninstall` (the script-mode path) already handles the layout
correctly via its own walk; only this manual fallback needed updating.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -327,9 +327,18 @@ If you don't have the repo cloned (e.g. you installed via a Claude Code paste an
 # 1. Stop browse daemons
 pkill -f "gstack.*browse" 2>/dev/null || true
 
-# 2. Remove per-skill symlinks pointing into gstack/
-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 "$link" ;; esac
+# 2. Remove per-skill directories whose SKILL.md points into gstack/
+find ~/.claude/skills -mindepth 1 -maxdepth 1 -type d ! -name gstack 2>/dev/null |
+while IFS= read -r dir; do
+  link="$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
 
 # 3. Remove gstack