feat: add /autocompleter endpoint for search suggestions

Proxies to upstream SearXNG /autocompleter if configured, otherwise
falls back to Wikipedia OpenSearch API. Returns a JSON array of
suggestion strings.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cmd/searxng-go/main.go

@@ -9,6 +9,7 @@ import (
 	"net/http"
 	"os"
 
+	"github.com/metamorphosis-dev/kafka/internal/autocomplete"
 	"github.com/metamorphosis-dev/kafka/internal/cache"
 	"github.com/metamorphosis-dev/kafka/internal/config"
 	"github.com/metamorphosis-dev/kafka/internal/httpapi"
@@ -57,12 +58,15 @@ func main() {
 		Cache:       searchCache,
 	})
 
-	h := httpapi.NewHandler(svc)
+	acSvc := autocomplete.NewService(cfg.Upstream.URL, cfg.HTTPTimeout())
+
+	h := httpapi.NewHandler(svc, acSvc.Suggestions)
 
 	mux := http.NewServeMux()
 	mux.HandleFunc("/", h.Index)
 	mux.HandleFunc("/healthz", h.Healthz)
 	mux.HandleFunc("/search", h.Search)
+	mux.HandleFunc("/autocompleter", h.Autocompleter)
 	mux.HandleFunc("/opensearch.xml", h.OpenSearch(cfg.Server.BaseURL))
 
 	// Serve embedded static files (CSS, JS, images).