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>

docs/website-api/openapi.json

@@ -24,6 +24,9 @@
     {
       "name": "Tenant"
     },
+    {
+      "name": "SEO"
+    },
     {
       "name": "Homepage"
     },
@@ -186,6 +189,81 @@
         }
       }
     },
+    "/tenants/{domain}/sitemap.xml": {
+      "get": {
+        "tags": [
+          "SEO"
+        ],
+        "summary": "XML sitemap for search engines",
+        "description": "Published products, blogs, and portfolios for this tenant (respects enabled modules), plus static pages and URL templates from the synced website manifest (`GET https://{domain}/meshkee/sitemap-config.json`). Default paths when not synced: `/`, `/products/{slug}`, `/blog/{slug}`, `/portfolios/{slug}`. Proxied from `https://{domain}/sitemap.xml` on the storefront. Cached in Redis; refreshed after CMS writes and manifest sync.",
+        "parameters": [
+          {
+            "$ref": "#/components/parameters/domain"
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "Sitemap XML (urlset)",
+            "content": {
+              "application/xml": {
+                "schema": {
+                  "type": "string"
+                }
+              }
+            },
+            "headers": {
+              "Cache-Control": {
+                "schema": {
+                  "type": "string",
+                  "example": "public, max-age=900"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Unknown domain"
+          }
+        }
+      }
+    },
+    "/tenants/{domain}/robots.txt": {
+      "get": {
+        "tags": [
+          "SEO"
+        ],
+        "summary": "robots.txt with sitemap reference",
+        "description": "Plain-text robots file pointing crawlers to `https://{domain}/sitemap.xml`. Proxied from `https://{domain}/robots.txt` on the storefront.",
+        "parameters": [
+          {
+            "$ref": "#/components/parameters/domain"
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "robots.txt",
+            "content": {
+              "text/plain": {
+                "schema": {
+                  "type": "string",
+                  "example": "User-agent: *\\nAllow: /\\n\\nSitemap: https://example.com/sitemap.xml\\n"
+                }
+              }
+            },
+            "headers": {
+              "Cache-Control": {
+                "schema": {
+                  "type": "string",
+                  "example": "public, max-age=900"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Unknown domain"
+          }
+        }
+      }
+    },
     "/tenants/{domain}/website/business-info": {
       "get": {
         "tags": [