Feat: RadioButtonGroup wrapping navigation for seamless cycling

Behavior:
- Vertical groups: Up/Down wrap around (down at end → first, up at start → last)
- Horizontal groups: Left/Right wrap around (right at end → first, left at start → last)
- Always return true (event consumed) — never falls through to FocusManager
- Enables smooth cycling through options without leaving the group

Implementation:
- Modified handleKeyEvent to use ternary wrap logic
- All navigation keys now always consumed (return true)
- Tab still exits group to next focusable element

Testing:
- Updated 'boundaryNavigation' test to verify wrapping behavior
- Test now checks that Up at start wraps to last item
- All 591 tests passing

User Experience:
- Stay in group when cycling options with arrow keys
- Tab exits to next group (standard radio group UX)

Sources/TUIkit/Views/RadioButton.swift

@@ -203,42 +203,34 @@ extension RadioButtonGroupHandler {
         case .up:
             // Up/Down only work for vertical orientation
             guard orientation == .vertical else { return false }
-            if focusedIndex > 0 {
-                focusedIndex -= 1
-                selection.wrappedValue = itemValues[focusedIndex]
-                return true
-            }
-            return false
+            // Wrap around: go to last item if at beginning
+            focusedIndex = focusedIndex > 0 ? focusedIndex - 1 : itemValues.count - 1
+            selection.wrappedValue = itemValues[focusedIndex]
+            return true
 
         case .down:
             // Up/Down only work for vertical orientation
             guard orientation == .vertical else { return false }
-            if focusedIndex < itemValues.count - 1 {
-                focusedIndex += 1
-                selection.wrappedValue = itemValues[focusedIndex]
-                return true
-            }
-            return false
+            // Wrap around: go to first item if at end
+            focusedIndex = focusedIndex < itemValues.count - 1 ? focusedIndex + 1 : 0
+            selection.wrappedValue = itemValues[focusedIndex]
+            return true
 
         case .left:
             // Left/Right only work for horizontal orientation
             guard orientation == .horizontal else { return false }
-            if focusedIndex > 0 {
-                focusedIndex -= 1
-                selection.wrappedValue = itemValues[focusedIndex]
-                return true
-            }
-            return false
+            // Wrap around: go to last item if at beginning
+            focusedIndex = focusedIndex > 0 ? focusedIndex - 1 : itemValues.count - 1
+            selection.wrappedValue = itemValues[focusedIndex]
+            return true
 
         case .right:
             // Left/Right only work for horizontal orientation
             guard orientation == .horizontal else { return false }
-            if focusedIndex < itemValues.count - 1 {
-                focusedIndex += 1
-                selection.wrappedValue = itemValues[focusedIndex]
-                return true
-            }
-            return false
+            // Wrap around: go to first item if at end
+            focusedIndex = focusedIndex < itemValues.count - 1 ? focusedIndex + 1 : 0
+            selection.wrappedValue = itemValues[focusedIndex]
+            return true
 
         case .enter, .character(" "):
             // Select current focused item

Tests/TUIkitTests/RadioButtonTests.swift

@@ -386,7 +386,7 @@ struct RadioButtonGroupHandlerTests {
         #expect(selection == AnyHashable("y"))
     }
 
-    @Test("Handler ignores boundary navigation")
+    @Test("Handler wraps navigation at boundaries")
     func boundaryNavigation() {
         var selection = AnyHashable("opt1")
         let binding = Binding(
@@ -403,12 +403,13 @@ struct RadioButtonGroupHandlerTests {
             canBeFocused: true
         )
 
-        // Try to go up from first item
+        // Try to go up from first item — should wrap to last
         let upEvent = KeyEvent(key: .up)
         let handled = handler.handleKeyEvent(upEvent)
 
-        #expect(handled == false)
-        #expect(handler.focusedIndex == 0)
+        #expect(handled == true)
+        #expect(handler.focusedIndex == 1)  // Wrapped to last item
+        #expect(selection == AnyHashable("opt2"))
     }
 
     @Test("Handler respects canBeFocused property")