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

backend/deploy/docker/Dockerfile.api-gateway

@@ -0,0 +1,32 @@
+# Build stage
+FROM golang:1.22-alpine AS builder
+
+RUN apk add --no-cache git ca-certificates
+
+WORKDIR /app
+
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+
+RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-s -w" -o /api-gateway ./cmd/api-gateway
+
+# Runtime stage
+FROM alpine:3.19
+
+RUN apk add --no-cache ca-certificates tzdata
+
+WORKDIR /app
+
+COPY --from=builder /api-gateway .
+
+ENV PORT=3015
+ENV GIN_MODE=release
+
+EXPOSE 3015
+
+HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
+    CMD wget --no-verbose --tries=1 --spider http://localhost:3015/health || exit 1
+
+CMD ["./api-gateway"]