pin react and next versions (#1233)

package.json

@@ -20,7 +20,7 @@
 		"@imgix/js-core": "^3.8.0",
 		"@mdx-js/loader": "^3.0.1",
 		"@mdx-js/react": "^3.0.1",
-		"@next/mdx": "rc",
+		"@next/mdx": "15.0.0-rc.0",
 		"@sindresorhus/slugify": "^2.2.1",
 		"@types/mdx": "^2.0.13",
 		"airtable": "^0.12.2",
@@ -36,9 +36,9 @@
 		"luxon": "^3.5.0",
 		"markdown-it": "^13.0.2",
 		"mdast-util-toc": "^7.1.0",
-		"next": "rc",
-		"react": "canary",
-		"react-dom": "canary",
+		"next": "15.0.0-rc.0",
+		"react": "19.0.0-rc-04bd67a4-20240924",
+		"react-dom": "19.0.0-rc-04bd67a4-20240924",
 		"react-leaflet": "^4.2.1",
 		"react-leaflet-cluster": "^2.1.0",
 		"rehype-autolink-headings": "^6.1.1",