docs: fix Next.js 14→15 references, add libs READMEs

- Fix remaining "Next.js 14" references in:
  - docs/architecture/IMPLEMENTATION_QUICK_REFERENCE.md
  - docs/load-testing/K6_LOAD_TESTING_GUIDE.md
- Create README.md for libs/ai-services/ (FastAPI AVM, moderation, NLP)
- Create README.md for libs/mcp-servers/ (MCP tool server library)
- Note: CLAUDE.md, README.md, and docs/architecture.md were already
  updated in a prior pass

Co-Authored-By: Paperclip <noreply@paperclip.ing>

docs/load-testing/K6_LOAD_TESTING_GUIDE.md

@@ -15,7 +15,7 @@
 ```
 goodgo-platform/
 ├── apps/api                 # NestJS backend (port 3001)
-├── apps/web                 # Next.js 14 frontend (port 3000)
+├── apps/web                 # Next.js 15 frontend (port 3000)
 ├── libs/mcp-servers         # MCP tool server library
 ├── prisma/                  # Database schema & migrations
 ├── e2e/                     # Playwright E2E tests (api + web)