fix: fast node creation, first-run modal, simplified docs

- Skip AI calls when no valid OpenAI key (fixes 9-13s timeout)
- Add first-run modal prompting for API key
- Rewrite README for first-time users
- Add /api/health endpoint
- Remove all Anthropic references (not used in OS)
- Fix bootstrap script (dev:local → dev)
- Fix next.config.js devIndicators warning
- Add Node 18+ version check

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/page.tsx

@@ -1,5 +1,11 @@
 import ThreePanelLayout from '@/components/layout/ThreePanelLayout';
+import FirstRunModal from '@/components/onboarding/FirstRunModal';
 
 export default function Home() {
-  return <ThreePanelLayout />;
+  return (
+    <>
+      <ThreePanelLayout />
+      <FirstRunModal />
+    </>
+  );
 }