Add public TabIndex to RadzenUpload on the Choose button

RadzenUpload inherits RadzenComponent, which has no TabIndex parameter,
so a tabindex value fell through the unmatched-attributes splat onto the
root wrapper div instead of the interactive Choose element. That made the
wrapper a dead focus stop and broke keyboard activation of the file
dialog. Add a public TabIndex parameter (mirroring FormComponent) and
apply it to the .rz-fileupload-choose span, which owns the keydown
handler, so tab order and Enter/Space activation work together.

Radzen.Blazor.Tests/UploadTests.cs

@@ -90,6 +90,44 @@ namespace Radzen.Blazor.Tests
 
             Assert.Contains("accept=\"image/*\"", component.Markup);
         }
+
+        [Fact]
+        public void Upload_Renders_DefaultTabIndex_OnChooseButton()
+        {
+            using var ctx = new TestContext();
+            ctx.JSInterop.Mode = JSRuntimeMode.Loose;
+            var component = ctx.RenderComponent<RadzenUpload>();
+
+            Assert.Equal("0", component.Find(".rz-fileupload-choose").GetAttribute("tabindex"));
+        }
+
+        [Fact]
+        public void Upload_Renders_TabIndex_OnChooseButton_NotWrapper()
+        {
+            using var ctx = new TestContext();
+            ctx.JSInterop.Mode = JSRuntimeMode.Loose;
+            var component = ctx.RenderComponent<RadzenUpload>(parameters =>
+            {
+                parameters.Add(p => p.TabIndex, 22);
+            });
+
+            Assert.Equal("22", component.Find(".rz-fileupload-choose").GetAttribute("tabindex"));
+            Assert.False(component.Find(".rz-fileupload").HasAttribute("tabindex"));
+        }
+
+        [Fact]
+        public void Upload_Renders_DisabledTabIndex_OnChooseButton()
+        {
+            using var ctx = new TestContext();
+            ctx.JSInterop.Mode = JSRuntimeMode.Loose;
+            var component = ctx.RenderComponent<RadzenUpload>(parameters =>
+            {
+                parameters.Add(p => p.TabIndex, 22);
+                parameters.Add(p => p.Disabled, true);
+            });
+
+            Assert.Equal("-1", component.Find(".rz-fileupload-choose").GetAttribute("tabindex"));
+        }
     }
 }
 

Radzen.Blazor/RadzenUpload.razor

@@ -8,7 +8,7 @@
 {
 <div @ref="@Element" style="@Style" @attributes="Attributes" class="@GetCssClass()" id="@GetId()">
     <div class="rz-fileupload-buttonbar">
-        <span class="@ChooseClassList" tabindex="@(Disabled ? -1 : 0)" role="button" aria-label="@ChooseText"
+        <span class="@ChooseClassList" tabindex="@(Disabled ? -1 : TabIndex)" role="button" aria-label="@ChooseText"
               aria-disabled="@(Disabled ? "true" : "false")" aria-controls="@(Name ?? GetId())"
               >
             @RenderInput()

Radzen.Blazor/RadzenUpload.razor.cs

@@ -202,6 +202,15 @@ namespace Radzen.Blazor
         [Parameter]
         public bool Disabled { get; set; }
 
+        /// <summary>
+        /// Gets or sets the tab order index for keyboard navigation.
+        /// Controls the order in which the Choose button receives focus when the user presses the Tab key.
+        /// Lower values receive focus first. Use -1 to exclude from tab navigation.
+        /// </summary>
+        /// <value>The tab index. Default is 0 (natural tab order).</value>
+        [Parameter]
+        public int TabIndex { get; set; } = 0;
+
         /// <summary>
         /// Gets the choose class list.
         /// </summary>