Add spider detection gate to SSR server so that search engine
crawlers get full server-side rendering with fresh API data,
while regular users receive the static CSR app shell from disk.
- backend/app/spider_detection.py: Python spider detection module
- spider_detection.ts: TypeScript mirror of spider detection patterns
- server.ts: SSR gate — isSpider() check before dispatching to
Angular SSR engine; non-spiders get static index.html
- server.spec.ts: Added spider detection unit tests
- tsconfig.app.json: Include spider_detection.ts in compilation
- backend/app/models.py: Fix SQLAlchemy FK resolution (user_models import)
