fix: move @prisma/client to production dependencies

src/db.js imports @prisma/client at runtime, but it was listed under
devDependencies (likely merged with the `prisma` devDependency during
Task 1). A production install that omits dev dependencies would crash
on startup with a missing-module error. `prisma` (the CLI) stays a
devDependency.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

package.json

@@ -12,6 +12,7 @@
     "postinstall": "prisma generate"
   },
   "dependencies": {
+    "@prisma/client": "^6.19.3",
     "docx": "^9.7.1",
     "dotenv": "^17.4.2",
     "express": "^5.2.1",
@@ -29,7 +30,6 @@
     "uuid": "^14.0.1"
   },
   "devDependencies": {
-    "@prisma/client": "^6.19.3",
     "@vitejs/plugin-react": "^6.0.5",
     "prisma": "^6.19.3",
     "supertest": "^7.2.2",