fix(noora): keep multi-select dropdowns open on toggle

Describe here the purpose of your PR.

A user reported on Slack that the days-of-the-week dropdown in the project notifications “Configure schedule” modal closes after every checkbox toggle, which makes selecting more than one day painful. They have to reopen the dropdown each time and lose their place.

The schedule-days dropdown is rendered with close_on_select={false} and Noora’s Zag-based menu honors that for plain items, but the items have checkboxes (checked={...}) so they also mount the NooraDropdownCheckbox hook. That hook was hard-coded to dispatch phx:close-dropdown whenever the click target was the label rather than the checkbox box, overriding the parent’s close_on_select setting and closing the menu after every toggle.

Two small changes fix it:

• NooraDropdownCheckbox now reads the parent dropdown’s data-close-on-select and skips the close dispatch when it’s "false". Checkbox dropdowns behave like the rest of the menu: Zag’s closeOnSelect: false keeps the menu open, the hook no longer fights it.
• dropdown.ex and button_dropdown.ex now render data-close-on-select as an explicit to_string(@close_on_select). Phoenix would otherwise drop the attribute entirely when the value is false, leaving dataset.closeOnSelect as undefined on the JS side; rendering it as "true" / "false" makes the dataset value reliable for the new check (and is still compatible with getBooleanOption used by Dropdown.js).

The Noora JS bundle (priv/static/noora.js) is generated by aube run build, which the server’s asset pipeline runs during mix assets.setup / mix assets.build, so no committed bundle change is needed.

How to test locally

1. Run the server (mise run dev) and open a project’s Notifications page.
2. Click “Configure” next to the Schedule row to open the modal.
3. Open the “Repeat” dropdown and tick several days in a row. The dropdown should stay open and the selection should accumulate; clicking outside the menu still closes it as before.
4. Confirm other dropdowns that select a single value (Frequency, Time, and any non-checkbox dropdown in the app) still close on selection.