Was generative AI tooling used to co-author this PR?

• Yes claude sonnet

What

The "Custom" expiration option in the Add/Edit Task Store modal was stubbed out and disabled, with a TODO comment waiting for a datetime picker component. DateTimeInput already existed but wasn't wired up.

Current behaviour

The "Custom" radio card in the Expiration section is disabled. Users can only choose "Default (30 days)" or "Never" — there is no way to set an arbitrary expiration datetime via the UI.

Proposed change

Enables the "Custom" option and renders a DateTimeInput below the radio group when it is selected. The picker respects the user's selected Airflow timezone and enforces a min of the current time so past datetimes cannot be chosen. The selected datetime is sent to the core API as an ISO 8601 string. Edit mode hydrates the picker correctly when an existing entry has a specific expires_at.

The Save button remains disabled until a date is entered when "Custom" is selected.

Testing

Adding a new task store

After its added

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