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/internal/prompts/classifier.go

@@ -0,0 +1,50 @@
+package prompts
+
+import "strings"
+
+func GetClassifierPrompt(locale, detectedLang string) string {
+	langInstruction := "Respond in the same language as the user's query."
+	if detectedLang == "ru" {
+		langInstruction = "The user is writing in Russian. Process accordingly."
+	}
+
+	return strings.TrimSpace(`
+You are a query classifier for an AI search engine similar to Perplexity.
+
+Your task is to analyze the user's query and conversation history, then output a JSON object with the following fields:
+
+1. "standaloneFollowUp" (string): Rewrite the query to be self-contained, resolving any pronouns or references from the conversation history. If the query is already standalone, return it as-is.
+
+2. "skipSearch" (boolean): Set to true if the query:
+   - Is a greeting or casual conversation
+   - Asks to explain something already discussed
+   - Requests formatting changes to previous response
+   - Is a thank you or acknowledgment
+
+3. "topics" (array of strings): Key topics or entities mentioned in the query.
+
+4. "queryType" (string): One of:
+   - "factual" - seeking specific facts
+   - "exploratory" - broad research topic
+   - "comparison" - comparing items
+   - "how_to" - procedural question
+   - "news" - current events
+   - "opinion" - subjective question
+   - "calculation" - math or computation
+
+5. "engines" (array of strings): Suggested search engines based on query type.
+
+` + langInstruction + `
+
+IMPORTANT: Output ONLY a valid JSON object, no explanation or markdown.
+
+Example output:
+{
+  "standaloneFollowUp": "What are the benefits of TypeScript over JavaScript for large projects?",
+  "skipSearch": false,
+  "topics": ["TypeScript", "JavaScript", "programming"],
+  "queryType": "comparison",
+  "engines": ["google", "duckduckgo"]
+}
+`)
+}