feat: Valkey cache for search results

- Add internal/cache package using go-redis/v9 (Valkey-compatible)
- Cache keys are deterministic SHA-256 hashes of search parameters
- Cache wraps the Search() method: check cache → miss → execute → store
- Gracefully disabled if Valkey is unreachable or unconfigured
- Configurable TTL (default 5m), address, password, and DB index
- Environment variable overrides: VALKEY_ADDRESS, VALKEY_PASSWORD,
  VALKEY_DB, VALKEY_CACHE_TTL
- Structured JSON logging via slog throughout cache layer
- Refactored service.go: extract executeSearch() from Search() for clarity
- Update config.example.toml with [cache] section
- Add cache package tests (key generation, nop behavior)

cmd/searxng-go/main.go

@@ -4,9 +4,11 @@ import (
 	"flag"
 	"fmt"
 	"log"
+	"log/slog"
 	"net/http"
 	"os"
 
+	"github.com/ashie/gosearch/internal/cache"
 	"github.com/ashie/gosearch/internal/config"
 	"github.com/ashie/gosearch/internal/httpapi"
 	"github.com/ashie/gosearch/internal/search"
@@ -16,11 +18,24 @@ func main() {
 	configPath := flag.String("config", "config.toml", "path to config.toml")
 	flag.Parse()
 
+	// Initialize structured logging.
+	logger := slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{Level: slog.LevelInfo}))
+	slog.SetDefault(logger)
+
 	cfg, err := config.Load(*configPath)
 	if err != nil {
 		log.Fatalf("failed to load config: %v", err)
 	}
 
+	// Initialize Valkey cache.
+	searchCache := cache.New(cache.Config{
+		Address:    cfg.Cache.Address,
+		Password:   cfg.Cache.Password,
+		DB:         cfg.Cache.DB,
+		DefaultTTL: cfg.CacheTTL(),
+	}, logger)
+	defer searchCache.Close()
+
 	// Seed env vars from config so existing engine/factory/planner code
 	// picks them up without changes. The config layer is the single source
 	// of truth; env vars remain as overrides via applyEnvOverrides.
@@ -37,6 +52,7 @@ func main() {
 	svc := search.NewService(search.ServiceConfig{
 		UpstreamURL: cfg.Upstream.URL,
 		HTTPTimeout: cfg.HTTPTimeout(),
+		Cache:       searchCache,
 	})
 
 	h := httpapi.NewHandler(svc)
@@ -46,6 +62,6 @@ func main() {
 	mux.HandleFunc("/search", h.Search)
 
 	addr := fmt.Sprintf(":%d", cfg.Server.Port)
-	log.Printf("searxng-go listening on %s", addr)
+	logger.Info("searxng-go starting", "addr", addr, "cache", searchCache.Enabled())
 	log.Fatal(http.ListenAndServe(addr, mux))
 }