Fix seed.ts module resolution: move to backend/prisma/

ts-node resolved node_modules relative to the script path, so running
from prisma/seed.ts (outside backend/) never found bcryptjs or
@prisma/client in backend/node_modules — the seed silently failed on
every container start. Moving the script under backend/prisma/ fixes
resolution; also adds a missing .gitignore for node_modules.

.gitignore

@@ -0,0 +1,4 @@
+node_modules/
+dist/
+.env
+*.log

backend/package.json

@@ -3,7 +3,7 @@
   "version": "1.0.0",
   "private": true,
   "prisma": {
-    "seed": "ts-node ../prisma/seed.ts"
+    "seed": "ts-node prisma/seed.ts"
   },
   "scripts": {
     "dev": "ts-node-dev --respawn -r dotenv/config src/app.ts",