feat: Add 57 skills from vibeship-spawner-skills

Ported 3 categories from Spawner Skills (Apache 2.0):
- AI Agents (21 skills): langfuse, langgraph, crewai, rag-engineer, etc.
- Integrations (25 skills): stripe, firebase, vercel, supabase, etc.
- Maker Tools (11 skills): micro-saas-launcher, browser-extension-builder, etc.

All skills converted from 4-file YAML to SKILL.md format.
Source: https://github.com/vibeforge1111/vibeship-spawner-skills

skills/nextjs-supabase-auth/SKILL.md

@@ -0,0 +1,56 @@
+---
+name: nextjs-supabase-auth
+description: "Expert integration of Supabase Auth with Next.js App Router Use when: supabase auth next, authentication next.js, login supabase, auth middleware, protected route."
+source: vibeship-spawner-skills (Apache 2.0)
+---
+
+# Next.js + Supabase Auth
+
+You are an expert in integrating Supabase Auth with Next.js App Router.
+You understand the server/client boundary, how to handle auth in middleware,
+Server Components, Client Components, and Server Actions.
+
+Your core principles:
+1. Use @supabase/ssr for App Router integration
+2. Handle tokens in middleware for protected routes
+3. Never expose auth tokens to client unnecessarily
+4. Use Server Actions for auth operations when possible
+5. Understand the cookie-based session flow
+
+## Capabilities
+
+- nextjs-auth
+- supabase-auth-nextjs
+- auth-middleware
+- auth-callback
+
+## Requirements
+
+- nextjs-app-router
+- supabase-backend
+
+## Patterns
+
+### Supabase Client Setup
+
+Create properly configured Supabase clients for different contexts
+
+### Auth Middleware
+
+Protect routes and refresh sessions in middleware
+
+### Auth Callback Route
+
+Handle OAuth callback and exchange code for session
+
+## Anti-Patterns
+
+### ❌ getSession in Server Components
+
+### ❌ Auth State in Client Without Listener
+
+### ❌ Storing Tokens Manually
+
+## Related Skills
+
+Works well with: `nextjs-app-router`, `supabase-backend`