Upgrade to Prisma 7 and clear npm audit advisories

- Prisma 5.22 -> 7.10 using the @prisma/adapter-pg driver adapter; the
  datasource URL moves to backend/prisma.config.js. All clients are built
  in src/config/db.js, and index.js reuses the shared client.
- Backend: patch follow-redirects, drop nodemon for `node --watch`, and use
  js-yaml 4 for the Jest coverage loader. npm audit reports 0.
- Frontend: override postcss-selector-parser to 7.1.7 (Tailwind 3 output
  is unchanged). braces has no patched release and stays, build/lint only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/scripts/migrate-env-to-db.js

@@ -24,7 +24,7 @@ const dotenv = require('dotenv');
 // Load .env from the backend root
 dotenv.config({ path: path.resolve(__dirname, '../.env') });
 
-const { PrismaClient } = require('@prisma/client');
+const { createPrismaClient } = require('../src/config/db');
 const crypto = require('crypto');
 
 const DRY_RUN = process.argv.includes('--dry-run');
@@ -90,7 +90,7 @@ const MAPPINGS = [
 // ─── Main ─────────────────────────────────────────────────────────────────────
 
 async function main() {
-  const prisma = new PrismaClient();
+  const prisma = createPrismaClient();
 
   console.log(`\n${'─'.repeat(60)}`);
   console.log('  Settings migration: .env → DB');

backend/scripts/seed-users.js

@@ -3,10 +3,11 @@
  * Run: node scripts/seed-users.js
  */
 
-const { PrismaClient } = require('@prisma/client');
+require('dotenv').config({ path: require('path').resolve(__dirname, '../.env') });
+const { createPrismaClient } = require('../src/config/db');
 const bcrypt = require('bcryptjs');
 
-const prisma = new PrismaClient();
+const prisma = createPrismaClient();
 
 const firstNames = [
   'Liam', 'Olivia', 'Noah', 'Emma', 'James', 'Ava', 'Elijah', 'Sophia',