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/webui/public/logo.svg

@@ -0,0 +1,12 @@
+<svg width="40" height="40" viewBox="0 0 40 40" fill="none" xmlns="http://www.w3.org/2000/svg">
+  <rect width="40" height="40" rx="10" fill="url(#gradient)"/>
+  <path d="M20 10L26 16L20 22L14 16L20 10Z" fill="#0a1929"/>
+  <path d="M14 20L20 26L26 20L20 14L14 20Z" fill="#0a1929" opacity="0.7"/>
+  <path d="M20 22L26 28L20 34L14 28L20 22Z" fill="#0a1929" opacity="0.5"/>
+  <defs>
+    <linearGradient id="gradient" x1="0" y1="0" x2="40" y2="40" gradientUnits="userSpaceOnUse">
+      <stop stop-color="#d4a373"/>
+      <stop offset="1" stop-color="#cd7f32"/>
+    </linearGradient>
+  </defs>
+</svg>