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/crossref_test.go

@@ -0,0 +1,71 @@
+package engines
+
+import (
+	"context"
+	"net/http"
+	"testing"
+
+	"github.com/ashie/gosearch/internal/contracts"
+)
+
+func TestCrossrefEngine_Search(t *testing.T) {
+	transport := roundTripperFunc(func(r *http.Request) (*http.Response, error) {
+		if r.Method != http.MethodGet {
+			return httpResponse(http.StatusMethodNotAllowed, "", ""), nil
+		}
+		if r.URL.Host != "api.crossref.org" || r.URL.Path != "/works" {
+			return httpResponse(http.StatusNotFound, "", ""), nil
+		}
+		q := r.URL.Query().Get("query")
+		if q != "hugo" {
+			return httpResponse(http.StatusBadRequest, "", ""), nil
+		}
+
+		body := `{
+  "message": {
+    "items": [
+      {
+        "type": "journal-article",
+        "title": ["Paper B"],
+        "URL": "https://example.com/paperb",
+        "abstract": "Abstract B",
+        "DOI": "10.1234/b",
+        "published": {
+          "date-parts": [[2020, 5, 1]]
+        }
+      }
+    ]
+  }
+}`
+		return httpResponse(http.StatusOK, body, "application/json"), nil
+	})
+
+	client := &http.Client{Transport: transport}
+	engine := &CrossrefEngine{client: client}
+
+	resp, err := engine.Search(context.Background(), contracts.SearchRequest{
+		Query:  "hugo",
+		Pageno: 1,
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(resp.Results) != 1 {
+		t.Fatalf("expected 1 result, got %d", len(resp.Results))
+	}
+
+	r := resp.Results[0]
+	if r.Title != "Paper B" {
+		t.Fatalf("expected title Paper B, got %q", r.Title)
+	}
+	if r.Content != "Abstract B" {
+		t.Fatalf("expected content, got %q", r.Content)
+	}
+	if r.Pubdate == nil || *r.Pubdate == "" {
+		t.Fatalf("expected pubdate, got nil/empty")
+	}
+	if r.Engine != "crossref" {
+		t.Fatalf("expected engine crossref, got %q", r.Engine)
+	}
+}
+