Ship prebuilt Prisma client so the server never runs prisma generate

prisma generate needs over three minutes on the production host, which made
every deploy hang on that build step. The client is now generated on the dev
machine into prisma-client.tar.gz (tracked, 8.5MB) and the image just untars
it. Dropping the unused linux-musl engine target halves that payload.

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

prisma/schema.prisma

@@ -1,6 +1,6 @@
 generator client {
   provider      = "prisma-client-js"
-  binaryTargets = ["native", "debian-openssl-3.0.x", "linux-musl-openssl-3.0.x"]
+  binaryTargets = ["native", "debian-openssl-3.0.x"]
 }
 
 datasource db {