Add Dynamic Sitemap & Robots.txt to Next.js (Cursor Prompt)

Add a dynamic sitemap and robots.txt to this Next.js App Router project.

FILES TO CREATE:
- src/app/sitemap.ts — Dynamic sitemap generation
- src/app/robots.ts — Robots.txt configuration

IMPLEMENTATION:
1. In sitemap.ts, export a default async function that returns MetadataRoute.Sitemap.
2. Include static routes with their priorities and change frequencies:
   - Home (/): priority 1.0, changeFrequency 'weekly'
   - About, Pricing, Contact: priority 0.8, changeFrequency 'monthly'
3. Fetch dynamic routes from Supabase:
   - Blog posts: query "blog_posts" for published posts, map to /blog/[slug] with priority 0.7
   - Product/listing pages: query relevant tables, map to /[type]/[slug] with priority 0.6
   - Set lastModified from the updated_at column
4. Combine static and dynamic routes into one array.
5. In robots.ts, export a default function returning MetadataRoute.Robots:
   - Allow all crawlers on all public paths
   - Disallow: /admin/*, /api/*, /auth/*
   - Point sitemap to: https://yourdomain.com/sitemap.xml
6. Add a sitemap index if you have more than 50,000 URLs by splitting into multiple sitemap files.

DO NOT:
- Include auth pages, admin pages, or API routes in the sitemap
- Include draft or unpublished content
- Hardcode the domain — use NEXT_PUBLIC_SITE_URL environment variable
- Use third-party sitemap generators

ENVIRONMENT VARIABLES:
- NEXT_PUBLIC_SITE_URL (e.g., https://yourdomain.com)