fix(setup): alias skills install as rewritten copies, never symlinks

The two back-compat alias dirs — _gstack-command (root router) and
connect-chrome (→ open-gstack-browser) — symlinked the canonical SKILL.md
verbatim, so each alias re-served the canonical frontmatter name:. Claude
Code keys skills on that name and requires global uniqueness: the
connect-chrome duplicate silently shadowed /open-gstack-browser (whichever
readdir returned first won), and the _gstack-command duplicate could drop
the ENTIRE personal-skills set — every /gstack command vanished until the
user hand-deleted the alias dirs, and the next setup re-broke it.

Fix: copy-then-rewrite. A shared _install_alias_skill_md helper reads the
SOURCE SKILL.md and writes a fresh copy with name: rewritten to the alias
dir's own name (_gstack-command / connect-chrome / gstack-connect-chrome).
sed never edits in place: on Unix the old install was a symlink into the
repo, and an in-place rewrite through it would have corrupted the generated
source (eng review E2). bin/gstack-relink gets the same treatment for its
root-alias helper, and its discovery loop now skips symlinked source dirs
so the connect-chrome repo symlink can't re-mint the duplicate.

Tests assert: installed aliases are NOT symlinks, carry their own unique
names, all installed frontmatter names are globally unique, re-runs refresh
cleanly, legacy symlinked aliases are replaced not written through, and the
source files stay byte-intact.

Fixes #2511
Fixes #2201

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bin/gstack-relink

@@ -52,7 +52,13 @@ _link_root_skill_alias() {
   [ -f "$INSTALL_DIR/SKILL.md" ] || return 0
   [ -L "$target" ] && rm -f "$target"
   mkdir -p "$target"
-  ln -snf "$INSTALL_DIR/SKILL.md" "$target/SKILL.md"
+  # Copy-then-rewrite, never a symlink (#2511): a symlinked alias re-serves
+  # the canonical `name: gstack`, Claude Code sees a duplicate skill name,
+  # and drops the ENTIRE personal-skills set. sed reads the source and writes
+  # a fresh copy — remove any prior symlink first so the redirect can never
+  # write through it into the generated source.
+  rm -f "$target/SKILL.md"
+  sed "1,/^---\$/ s/^name:[[:space:]].*/name: _gstack-command/" "$INSTALL_DIR/SKILL.md" > "$target/SKILL.md"
 }
 
 _link_root_skill_alias
@@ -61,6 +67,11 @@ _link_root_skill_alias
 SKILL_COUNT=0
 for skill_dir in "$INSTALL_DIR"/*/; do
   [ -d "$skill_dir" ] || continue
+  # Skip symlinked skill dirs (connect-chrome → open-gstack-browser): linking
+  # one under the symlink's basename would duplicate the canonical frontmatter
+  # name and collide in Claude Code's skill registry (#2201). setup owns the
+  # rewritten-copy alias for those.
+  [ -L "${skill_dir%/}" ] && continue
   skill=$(basename "$skill_dir")
   # Skip non-skill directories
   case "$skill" in bin|browse|design|docs|extension|lib|node_modules|scripts|test|.git|.github) continue ;; esac