fix: resolve race conditions and update golangci-lint config

- Fix TestCertificateHandler_Delete race condition:
  - Add WAL mode and busy_timeout to SQLite connection
  - Add sleep to allow background sync goroutine to complete
- Fix TestNotificationService_SendExternal_EdgeCases race condition:
  - Use atomic.Value for cross-goroutine string access
- Update .golangci.yml for version 2:
  - Add version field
  - Move linters-settings under linters.settings
  - Remove deprecated typecheck and gosimple linters
  - Update govet shadow check syntax

backend/.golangci.yml

@@ -0,0 +1,35 @@
+version: "2"
+
+run:
+  timeout: 5m
+  tests: true
+
+linters:
+  enable:
+    - bodyclose
+    - gocritic
+    - gosec
+    - govet
+    - ineffassign
+    - staticcheck
+    - unused
+    - revive
+
+  settings:
+    gocritic:
+      enabled-tags:
+        - diagnostic
+        - experimental
+        - opinionated
+        - performance
+        - style
+      disabled-checks:
+        - whyNoLint
+        - wrapperFunc
+    govet:
+      enable:
+        - shadow
+    revive:
+      rules:
+        - name: exported
+          severity: warning

backend/internal/api/handlers/certificate_handler_test.go

@@ -133,7 +133,8 @@ func TestCertificateHandler_Upload(t *testing.T) {
 func TestCertificateHandler_Delete(t *testing.T) {
 	// Setup
 	tmpDir := t.TempDir()
-	db, err := gorm.Open(sqlite.Open("file::memory:?cache=shared"), &gorm.Config{})
+	// Use WAL mode and busy timeout for better concurrency with race detector
+	db, err := gorm.Open(sqlite.Open("file::memory:?cache=shared&_journal_mode=WAL&_busy_timeout=5000"), &gorm.Config{})
 	require.NoError(t, err)
 	require.NoError(t, db.AutoMigrate(&models.SSLCertificate{}))
 
@@ -147,6 +148,8 @@ func TestCertificateHandler_Delete(t *testing.T) {
 	require.NotZero(t, cert.ID)
 
 	service := services.NewCertificateService(tmpDir, db)
+	// Allow background sync goroutine to complete before testing
+	time.Sleep(50 * time.Millisecond)
 	ns := services.NewNotificationService(db)
 	handler := NewCertificateHandler(service, ns)
 

backend/internal/services/notification_service_test.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+	"sync/atomic"
 	"testing"
 	"time"
 
@@ -498,12 +499,13 @@ func TestNotificationService_SendExternal_EdgeCases(t *testing.T) {
 		db := setupNotificationTestDB(t)
 		svc := NewNotificationService(db)
 
-		receivedCustom := ""
+		var receivedCustom atomic.Value
+		receivedCustom.Store("")
 		ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			var body map[string]interface{}
 			json.NewDecoder(r.Body).Decode(&body)
 			if custom, ok := body["custom"]; ok {
-				receivedCustom = custom.(string)
+				receivedCustom.Store(custom.(string))
 			}
 			w.WriteHeader(http.StatusOK)
 		}))
@@ -525,7 +527,7 @@ func TestNotificationService_SendExternal_EdgeCases(t *testing.T) {
 		svc.SendExternal("proxy_host", "Title", "Message", customData)
 		time.Sleep(100 * time.Millisecond)
 
-		assert.Equal(t, "test-value", receivedCustom)
+		assert.Equal(t, "test-value", receivedCustom.Load().(string))
 	})
 }