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>

libs/ai-services/README.md

@@ -0,0 +1,69 @@
+# @goodgo/ai-services
+
+Python FastAPI AI/ML microservice for the GoodGo Platform.
+
+## Services
+
+| Service | Router | Description |
+|---------|--------|-------------|
+| **AVM** | `/avm` | Automated Valuation Model — XGBoost-based property price predictions |
+| **Moderation** | `/moderation` | Content moderation for listings (text + image analysis) |
+| **NLP** | `/nlp` | Vietnamese NLP — feature extraction, search query understanding |
+
+## Tech Stack
+
+- **Python** 3.12+
+- **FastAPI** 0.115 + Uvicorn
+- **XGBoost** 2.1 (property valuation model)
+- **Underthesea** 6.8 (Vietnamese NLP tokenizer)
+- **Pydantic** 2.9 (request/response schemas)
+
+## Quick Start
+
+```bash
+# Via Docker (recommended — runs as part of the platform stack)
+docker compose up -d ai-services
+
+# Standalone
+cd libs/ai-services
+pip install -e ".[dev]"
+uvicorn app.main:app --reload --port 8000
+```
+
+## Project Structure
+
+```
+libs/ai-services/
+├── app/
+│   ├── main.py          # FastAPI app entry point
+│   ├── config.py        # Settings (Pydantic BaseSettings)
+│   ├── middleware.py     # CORS, rate limiting, error handling
+│   ├── models/          # Pydantic request/response schemas
+│   │   ├── avm.py
+│   │   ├── moderation.py
+│   │   └── nlp.py
+│   ├── routers/         # API route handlers
+│   │   ├── avm.py
+│   │   ├── moderation.py
+│   │   └── nlp.py
+│   └── services/        # Business logic
+│       ├── avm_service.py
+│       ├── moderation_service.py
+│       └── nlp_service.py
+├── tests/               # pytest test suite
+├── Dockerfile           # Production container image
+└── pyproject.toml       # Dependencies and config
+```
+
+## Testing
+
+```bash
+cd libs/ai-services
+pytest
+```
+
+## Health Check
+
+```
+GET /health → {"status": "ok"}
+```