Fix: Preserve null value for expire parameter in ExpirationInput

- Fixed reactive block in expirationInput.svelte to check for null before converting to ISO date
- When "Never" is selected, value now remains null instead of being converted to '1970-01-01'
- This allows the API to correctly handle null expiration dates for API keys and file tokens

Co-authored-by: stnguyen90 <1477010+stnguyen90@users.noreply.github.com>

Author: Copilot

src/lib/components/expirationInput.svelte

@@ -134,7 +134,10 @@
             value = expirationSelect === 'custom' ? expirationCustom : expirationSelect;
         }
 
-        value = toLocaleDateISO(new Date(value).getTime());
+        // Only convert to ISO date if value is not null
+        if (value !== null) {
+            value = toLocaleDateISO(new Date(value).getTime());
+        }
     }
 
     $: helper =