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)
- ThemeService: remove isPlatformBrowser guard so CSS custom properties
are applied during SSR/prerender — server-rendered HTML now carries the
correct color scheme and gradients (fixes missing colors on test site).
- main.ts: add provideClientHydration() so Angular preserves the server-
rendered DOM on the client instead of destroying and rebuilding it
(fixes jarring full-page reload between static and dynamic versions).
- Tests: update theme.service.spec.ts to match new behaviour, expand
coverage with gradient tests and empty-value handling (9 tests).
Fix structured-data.component.spec.ts import paths. All 54 tests pass.