[Fix] Key Expiry: omit duration from payload when not set by user

- create_key_button: remove initialValue={null} on hidden duration field;
  change submit handler to delete duration when empty/undefined rather than
  converting to null, so untouched expiry settings don't accidentally trigger
  never-expires behavior on the backend.
- key_edit_view: remove initialValue="" on hidden duration field; add same
  duration cleanup to handleSubmit so an untouched field sends no duration
  key instead of an empty string.
- In both cases duration: null is preserved (Never Expires checkbox).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/litellm-dashboard/src/components/organisms/create_key_button.tsx

@@ -350,9 +350,11 @@ const CreateKey: React.FC<CreateKeyProps> = ({ team, teams, data, addKey }) => {
         formValues.rotation_interval = rotationInterval;
       }
 
-      // Handle duration field for key expiry - convert empty string to null
-      if (!formValues.duration || formValues.duration.trim() === "") {
-        formValues.duration = null;
+      // Handle duration field for key expiry:
+      // - null means Never Expires (explicitly set by checkbox) — keep as-is
+      // - empty string or undefined means not provided — omit entirely
+      if (formValues.duration !== null && (!formValues.duration || formValues.duration.trim() === "")) {
+        delete formValues.duration;
       }
 
       // Update the formValues with the final metadata
@@ -1407,7 +1409,7 @@ const CreateKey: React.FC<CreateKeyProps> = ({ team, teams, data, addKey }) => {
                         />
                       </div>
                     </AccordionBody>
-                    <Form.Item name="duration" hidden initialValue={null}>
+                    <Form.Item name="duration" hidden>
                       <Input />
                     </Form.Item>
                   </Accordion>

ui/litellm-dashboard/src/components/templates/key_edit_view.tsx

@@ -263,6 +263,11 @@ export function KeyEditView({
       }
       // If it's already an array (shouldn't happen, but handle it), keep as is
 
+      // Handle duration: null = Never Expires (keep); empty string or undefined = not changed (omit)
+      if (values.duration !== null && (!values.duration || values.duration.trim() === "")) {
+        delete values.duration;
+      }
+
       await onSubmit(values);
     } finally {
       setIsKeySaving(false);
@@ -659,7 +664,7 @@ export function KeyEditView({
           rotationInterval={rotationInterval}
           onRotationIntervalChange={setRotationInterval}
         />
-        <Form.Item name="duration" hidden initialValue="">
+        <Form.Item name="duration" hidden>
           <Input />
         </Form.Item>
       </div>