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

.gitignore

@@ -44,4 +44,7 @@ certificates
 
 # SSL backup (приватные ключи не в репо)
 deploy/k3s/ssl/backup/*
-!deploy/k3s/ssl/backup/.gitkeep
+!deploy/k3s/ssl/backup/.gitkeep
+
+# Vendor cache (npm + Docker images для оффлайн-билда)
+vendor/