feat: add local dev mode for testing skills from within the repo

bin/dev-setup creates .claude/skills/gstack symlink to the working tree
so Claude Code discovers skills locally. bin/dev-teardown cleans up.
DEVELOPING_GSTACK.md documents the workflow.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

bin/dev-teardown

@@ -0,0 +1,39 @@
+#!/usr/bin/env bash
+# Remove local dev skill symlinks. Restores global gstack as the active install.
+set -e
+
+REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+SKILLS_DIR="$REPO_ROOT/.claude/skills"
+
+if [ ! -d "$SKILLS_DIR" ]; then
+  echo "Nothing to tear down — .claude/skills/ doesn't exist."
+  exit 0
+fi
+
+# Remove individual skill symlinks
+removed=()
+for link in "$SKILLS_DIR"/*/; do
+  name="$(basename "$link")"
+  [ "$name" = "gstack" ] && continue
+  if [ -L "${link%/}" ]; then
+    rm "${link%/}"
+    removed+=("$name")
+  fi
+done
+
+# Remove the gstack symlink
+if [ -L "$SKILLS_DIR/gstack" ]; then
+  rm "$SKILLS_DIR/gstack"
+  removed+=("gstack")
+fi
+
+# Clean up empty dirs
+rmdir "$SKILLS_DIR" 2>/dev/null || true
+rmdir "$REPO_ROOT/.claude" 2>/dev/null || true
+
+if [ ${#removed[@]} -gt 0 ]; then
+  echo "Removed: ${removed[*]}"
+else
+  echo "No symlinks found."
+fi
+echo "Dev mode deactivated. Global gstack (~/.claude/skills/gstack) is now active."