fix: Add missing locales on SK date picker

[AyakorK]

🎩 Description

On the Banska platform (sk locale), the admin datepicker displayed undefined in several places (help text, aria-labels, calendar close button), and in some cases blocked event creation/editing entirely (validation stuck on date fields).

The datepicker JS component (generate_datepicker.js / form_date_picker.js) fetches its translations via getDictionary() on the date.formats, time, and date.buttons keys. These keys were missing from sk.yml, so the JS received undefined instead of a string and rendered it as-is in the DOM.

Testing

• Log in as admin on an organization with the sk locale active
• Create or edit an event or assembly (any form with a date field)
• Check that the help text under the datepicker shows readable text (no more undefined)
• Open the calendar, check that the close button shows text instead of undefined
• Pick a date and confirm it saves with the correct format (day/month not swapped)

Note: local reproduction is possible but kind of hard, since many other sk.yml keys are missing beyond the datepicker ones, there's no clean way to isolate just sk for testing. Testing was done by adding temporary locales that were deleted afterwards

📌 Related Issues

• Fixes https://github.com/orgs/OpenSourcePolitics/projects/26/views/1?pane=issue&itemId=214146921&issue=OpenSourcePolitics%7Cintern-tasks%7C469

Tasks

• Add missing locales