fix(lint): resolve golangci-lint errcheck and gofmt issues

- Add errcheck handling for w.Write, json.Encode in test handlers
- Use defer func() { _ = resp.Body.Close() }() pattern
- Use safe two-return type assertions in websearch_config.go
- Fix gofmt alignment in setting_service.go struct fields

backend/internal/pkg/websearch/brave.go

@@ -62,7 +62,7 @@ func (b *BraveProvider) Search(ctx context.Context, req SearchRequest) (*SearchR
 	if err != nil {
 		return nil, fmt.Errorf("brave: request failed: %w", err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	body, err := io.ReadAll(io.LimitReader(resp.Body, maxResponseSize))
 	if err != nil {

backend/internal/pkg/websearch/brave_test.go

@@ -29,7 +29,7 @@ func TestBraveProvider_Search_Success(t *testing.T) {
 			{URL: "https://tour.go.dev", Title: "Tour", Description: "A Tour of Go", Age: "3 days"},
 		}
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(resp)
+		_ = json.NewEncoder(w).Encode(resp)
 	}))
 	defer srv.Close()
 
@@ -53,7 +53,7 @@ func TestBraveProvider_Search_DefaultMaxResults(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		receivedCount = r.URL.Query().Get("count")
 		resp := braveResponse{}
-		json.NewEncoder(w).Encode(resp)
+		_ = json.NewEncoder(w).Encode(resp)
 	}))
 	defer srv.Close()
 
@@ -70,7 +70,7 @@ func TestBraveProvider_Search_DefaultMaxResults(t *testing.T) {
 func TestBraveProvider_Search_HTTPError(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
 		w.WriteHeader(429)
-		w.Write([]byte("rate limited"))
+		_, _ = w.Write([]byte("rate limited"))
 	}))
 	defer srv.Close()
 
@@ -86,7 +86,7 @@ func TestBraveProvider_Search_HTTPError(t *testing.T) {
 
 func TestBraveProvider_Search_InvalidJSON(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
-		w.Write([]byte("not json"))
+		_, _ = w.Write([]byte("not json"))
 	}))
 	defer srv.Close()
 
@@ -103,7 +103,7 @@ func TestBraveProvider_Search_InvalidJSON(t *testing.T) {
 func TestBraveProvider_Search_EmptyResults(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
 		resp := braveResponse{}
-		json.NewEncoder(w).Encode(resp)
+		_ = json.NewEncoder(w).Encode(resp)
 	}))
 	defer srv.Close()
 

backend/internal/pkg/websearch/tavily.go

@@ -60,7 +60,7 @@ func (t *TavilyProvider) Search(ctx context.Context, req SearchRequest) (*Search
 	if err != nil {
 		return nil, fmt.Errorf("tavily: request failed: %w", err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	body, err := io.ReadAll(io.LimitReader(resp.Body, maxResponseSize))
 	if err != nil {

backend/internal/service/setting_service.go

@@ -105,8 +105,8 @@ type SettingService struct {
 	settingRepo           SettingRepository
 	defaultSubGroupReader DefaultSubscriptionGroupReader
 	cfg                   *config.Config
-	onUpdate              func() // Callback when settings are updated (for cache invalidation)
-	version               string // Application version
+	onUpdate              func()        // Callback when settings are updated (for cache invalidation)
+	version               string        // Application version
 	webSearchRedis        *redis.Client // optional: Redis client for web search quota tracking
 }
 

backend/internal/service/websearch_config.go

@@ -96,8 +96,7 @@ const (
 // GetWebSearchEmulationConfig returns the configuration with in-process cache + singleflight.
 func (s *SettingService) GetWebSearchEmulationConfig(ctx context.Context) (*WebSearchEmulationConfig, error) {
 	if cached := webSearchEmulationCache.Load(); cached != nil {
-		c := cached.(*cachedWebSearchEmulationConfig)
-		if time.Now().UnixNano() < c.expiresAt {
+		if c, ok := cached.(*cachedWebSearchEmulationConfig); ok && time.Now().UnixNano() < c.expiresAt {
 			return c.config, nil
 		}
 	}
@@ -107,7 +106,10 @@ func (s *SettingService) GetWebSearchEmulationConfig(ctx context.Context) (*WebS
 	if err != nil {
 		return &WebSearchEmulationConfig{}, err
 	}
-	return result.(*WebSearchEmulationConfig), nil
+	if cfg, ok := result.(*WebSearchEmulationConfig); ok {
+		return cfg, nil
+	}
+	return &WebSearchEmulationConfig{}, nil
 }
 
 func (s *SettingService) loadWebSearchConfigFromDB() (*WebSearchEmulationConfig, error) {