Sostituita ricerca web SearXNG con Chromium/Bing; rimossa UI gestione istanze

Fix: ricerca web – istanze casuali, fallback Wikipedia, fix path MEGA DB

Add remaining instances from user list (gruble, failsearx, ricerca.2b9t, etc.)

Add 60+ hardcoded instances + merge with searx.space API list

Fix instance check: detect online/JSON-disabled/offline correctly, update instance list

Add brave, bing(edge), torch engines to SearXNG + /engines endpoint

Add /instances/select and /instances/active to switch SearXNG at runtime

Switch search: DuckDuckGo -> SearXNG (multi-instance fallback)

Full AI stack: brain, knowledge_base, scraper, seed — FastAPI wrapper