Add GitHub Actions workflow and health check for API

[Zero-Sugar0]

This PR introduces a lightweight health check endpoint at /api/health.

• Implements GET handler in app/api/health/route.ts
• Returns a simple 200 OK JSON response
• Provides a target for QStash keep-alive pings every 14 minutes
• Ensures Render free-tier service does not idle after 15 minutes of inactivity

This endpoint is intentionally minimal to avoid triggering agent logic and is designed solely for uptime monitoring.