feat: build Go-based SearXNG-compatible search service

Implement an API-first Go rewrite with local engine adapters, upstream fallback, and Nix-based tooling so searches can run without matching the original UI while preserving response compatibility.

Made-with: Cursor

internal/engines/factory.go

@@ -0,0 +1,33 @@
+package engines
+
+import (
+	"net/http"
+	"os"
+	"time"
+)
+
+// NewDefaultPortedEngines returns the starter set of Go-native engines.
+// The service can swap/extend this registry later as more engines are ported.
+func NewDefaultPortedEngines(client *http.Client) map[string]Engine {
+	if client == nil {
+		client = &http.Client{Timeout: 10 * time.Second}
+	}
+
+	return map[string]Engine{
+		"wikipedia": &WikipediaEngine{client: client},
+		"arxiv":     &ArxivEngine{client: client},
+		"crossref":  &CrossrefEngine{client: client},
+		"braveapi": &BraveEngine{
+			client:          client,
+			apiKey:          os.Getenv("BRAVE_API_KEY"),
+			accessGateToken: os.Getenv("BRAVE_ACCESS_TOKEN"),
+			resultsPerPage: 20,
+		},
+		"qwant": &QwantEngine{
+			client:         client,
+			category:       "web-lite",
+			resultsPerPage: 10,
+		},
+	}
+}
+