fix(response): add nil check for c.Request in error logging

Prevents panic when ErrorFrom is called in test contexts where
gin.CreateTestContext doesn't set up an HTTP request.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/internal/pkg/response/response.go

@@ -77,7 +77,7 @@ func ErrorFrom(c *gin.Context, err error) bool {
 	statusCode, status := infraerrors.ToHTTP(err)
 
 	// Log internal errors with full details for debugging
-	if statusCode >= 500 {
+	if statusCode >= 500 && c.Request != nil {
 		log.Printf("[ERROR] %s %s\n  Error: %s", c.Request.Method, c.Request.URL.Path, err.Error())
 	}