chore: bootstrap gstack team mode

Per gstack team-mode install: adds a PreToolUse hook that blocks
skill usage when gstack isn't installed globally, so contributors
are prompted to install it. Un-ignores the two required files
(.claude/settings.json, .claude/hooks/check-gstack.sh) while
keeping settings.local.json and other Claude state ignored.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.claude/hooks/check-gstack.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+# Block skill usage when gstack is not installed globally.
+
+if [ ! -d "$HOME/.claude/skills/gstack/bin" ]; then
+  cat >&2 <<'MSG'
+BLOCKED: gstack is not installed globally.
+
+gstack is required for AI-assisted work in this repo.
+
+Install it:
+  git clone --depth 1 https://github.com/garrytan/gstack.git ~/.claude/skills/gstack
+  cd ~/.claude/skills/gstack && ./setup --team
+
+Then restart your AI coding tool.
+MSG
+  echo '{"permissionDecision":"deny","message":"gstack is required but not installed. See stderr for install instructions."}'
+  exit 0
+fi
+
+echo '{}'

.claude/settings.json

@@ -0,0 +1,15 @@
+{
+  "hooks": {
+    "PreToolUse": [
+      {
+        "matcher": "Skill",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "\"$CLAUDE_PROJECT_DIR/.claude/hooks/check-gstack.sh\""
+          }
+        ]
+      }
+    ]
+  }
+}

.gitignore

@@ -207,7 +207,11 @@ marimo/_lsp/
 __marimo__/
 
 # Claude Code (local config, agents, settings)
-.claude/
+.claude/*
+!.claude/settings.json
+!.claude/hooks/
+.claude/hooks/*
+!.claude/hooks/check-gstack.sh
 .agents/
 
 # Database dumps