feat: Go backend, enhanced search, new widgets, Docker deploy

Major changes:
- Add Go backend (backend/) with microservices architecture
- Enhanced master-agents-svc: reranker, content-classifier, stealth-crawler,
  proxy-manager, media-search, fastClassifier, language detection
- New web-svc widgets: KnowledgeCard, ProductCard, ProfileCard, VideoCard,
  UnifiedCard, CardGallery, InlineImageGallery, SourcesPanel, RelatedQuestions
- Improved discover-svc with discover-db integration
- Docker deployment improvements (Caddyfile, vendor.sh, BUILD.md)
- Library-svc: project_id schema migration
- Remove deprecated finance-svc and travel-svc
- Localization improvements across services

Made-with: Cursor

deploy/docker/Dockerfile.caddy

@@ -0,0 +1,7 @@
+# Caddy 2 с плагином rate_limit для защиты от DDoS (per-IP лимиты)
+# Оригинал mholt/caddy-ratelimit (distributed через storage при необходимости)
+FROM caddy:2-builder AS builder
+RUN xcaddy build --with github.com/mholt/caddy-ratelimit
+
+FROM caddy:2-alpine
+COPY --from=builder /usr/bin/caddy /usr/bin/caddy