Implement official Prisma solution for client generation

Following Prisma's official documentation for deployment caching issues:
https://www.prisma.io/docs/orm/more/help-and-troubleshooting/vercel-caching-issue

Changes:
- Add 'prisma generate' to build script (official Prisma recommendation)
- Add postinstall script for automatic client generation
- Remove custom stub generator workaround
- Keep runtime Prisma client generation in entrypoint.sh for reliability
- Add openssl to runtime container (required for Prisma engines)

This follows Prisma best practices: explicitly run prisma generate during the
build process to ensure Prisma Client is always up-to-date. The entrypoint
script regenerates the client at runtime to guarantee engine availability in
the production environment.

package.json

@@ -5,11 +5,11 @@
   "private": true,
   "scripts": {
     "dev": "next dev",
-    "build": "node scripts/generate-prisma-stub.js && next build",
+    "build": "prisma generate && next build",
     "start": "next start",
     "lint": "next lint",
     "typecheck": "tsc --noEmit",
-    "postinstall": "node scripts/generate-prisma-stub.js || prisma generate || echo 'Prisma generate failed, using stub'"
+    "postinstall": "prisma generate || echo 'Prisma generate skipped'"
   },
   "dependencies": {
     "@emotion/react": "^11.14.0",