Initial commit: Sibilla — self-hosted Perplexity-like AI search engine

- Flask web app with Perplexity-style search + synthesis pipeline
- Degoog → SearXNG → DuckDuckGo cascading search backends
- Gemini LLM for query expansion + answer synthesis with citations
- MCP server exposing search tools via stdio
- 57 unit tests covering all modules

.env.example

@@ -1,7 +1,20 @@
 # Google AI API Key — ottenila da https://aistudio.google.com/apikey
 GOOGLE_API_KEY=your-api-key-here
 
-# Flask
+# ── Search backends (cascading: Degoog → SearXNG → DuckDuckGo) ──
+
+# Degoog (primary) — self-hosted metasearch, default port 4444
+# Avvia con: docker run -d --name degoog -p 4444:4444 ghcr.io/degoog-org/degoog:latest
+DEGOOG_URL=http://localhost:4444
+
+# SearXNG (fallback 1) — self-hosted metasearch, default port 8080
+# Avvia con: docker run -d -p 8080:8080 searxng/searxng
+SEARXNG_URL=http://localhost:8080
+
+# DuckDuckGo (fallback 2) — nessun server richiesto
+SIBILLA_DDG_FALLBACK=1
+
+# ── Flask ──
 SECRET_KEY=change-me-to-a-random-string
 SIBILLA_HOST=127.0.0.1
 SIBILLA_PORT=5000