chore: remove prisma-erd-generator and stale erd refs

Vercel detecteert @prisma/client en runt automatisch `prisma generate`
zonder --generator filter. Daardoor probeerde de erd-generator op Vercel
te draaien en faalde op libnss3.so (puppeteer/Chrome niet beschikbaar in
de build container). Cascading: de Prisma-client werd niet ge-update,
runtime kreeg oude enum-waarden (ACTIVE i.p.v. OPEN).

ERD is dev-only documentatie en niet meer in productie nodig. Generator
+ dependency + npm scripts + de gegenereerde svg verwijderd. README,
prisma-client pattern en architecture docs bijgewerkt.

Build script blijft `prisma generate && next build` zodat de client ook
bij Vercel build-cache-hits opnieuw wordt gegenereerd.

package.json

@@ -1,12 +1,12 @@
 {
   "name": "scrum4me",
-  "version": "1.2.0",
+  "version": "1.3.0",
   "private": true,
   "scripts": {
     "predev": "npx --yes kill-port 3000 || exit 0",
     "dev": "next dev -p 3000",
     "prebuild": "npm run manual:build",
-    "build": "next build",
+    "build": "prisma generate && next build",
     "start": "next start",
     "lint": "eslint",
     "typecheck": "tsc --noEmit",
@@ -15,8 +15,6 @@
     "test:watch": "vitest",
     "prepare": "husky",
     "postinstall": "prisma generate --generator client",
-    "db:erd": "prisma generate",
-    "db:erd:watch": "chokidar \"prisma/schema.prisma\" -c \"npm run db:erd\"",
     "db:insert-milestone": "tsx scripts/insert-milestone.ts",
     "db:sync-model-prices": "tsx scripts/sync-model-prices.ts",
     "create-admin": "tsx scripts/create-admin.ts",
@@ -88,14 +86,12 @@
     "@types/react-dom": "^19",
     "@types/web-push": "^3.6.4",
     "@vitest/coverage-v8": "^4.1.5",
-    "chokidar-cli": "^3.0.0",
     "concurrently": "^9.2.1",
     "eslint": "^9",
     "eslint-config-next": "16.2.4",
     "husky": "^9.1.7",
     "jsdom": "^29.1.1",
     "lint-staged": "^16.4.0",
-    "prisma-erd-generator": "^2.4.2",
     "tailwindcss": "^4",
     "tsx": "^4.21.0",
     "typescript": "^5",