fix: gracefully skip Sanity typegen when env vars unavailable

The prebuild typegen step fails on Vercel because sanity.config.ts
imports sanity/lib/api.ts which throws if NEXT_PUBLIC_SANITY_DATASET
and NEXT_PUBLIC_SANITY_PROJECT_ID are not set. Even though these are
configured in Vercel, they may not be available during the prebuild
phase.

This change makes typegen non-fatal — if it fails, the build continues
using the already-committed types in sanity/types.ts.

Author: Miriad

package.json

@@ -6,7 +6,7 @@
 		"start": "next start",
 		"lint": "biome check .",
 		"predev": "npm run typegen",
-		"prebuild": "npm run typegen",
+		"prebuild": "npx sanity schema extract --path=./sanity/extract.json && npx sanity typegen generate || echo 'Sanity typegen skipped (env vars not available)'",
 		"typegen": "sanity schema extract --path=./sanity/extract.json && sanity typegen generate",
 		"format": "biome format . --write"
 	},