Add backend-generated sitemap with website manifest sync and nginx SEO proxy support.

Stores synced route config from /meshkee/sitemap-config.json, serves sitemap.xml and robots.txt per tenant, and invalidates cache on CMS writes.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/sitemap/sitemap.constants.ts

@@ -0,0 +1,17 @@
+/** Safety-net TTL when invalidation is missed; normal freshness is event-driven. */
+export const SITEMAP_CACHE_TTL_SECONDS = 3600;
+
+export const SITEMAP_URLSET_NS = 'http://www.sitemaps.org/schemas/sitemap/0.9';
+
+/** Default storefront path templates (overridable via /meshkee/sitemap-config.json). */
+export const DEFAULT_SITEMAP_PATH_TEMPLATES = {
+  product: '/products/{slug}',
+  blog: '/blog/{slug}',
+  portfolio: '/portfolios/{slug}',
+} as const;
+
+export const WEBSITE_SITEMAP_CONFIG_PATH = '/meshkee/sitemap-config.json';
+
+export const DEFAULT_SITEMAP_STATIC_PAGES = [
+  { path: '/', changefreq: 'daily' as const, priority: 1.0 },
+] as const;