Closes #311

Note:

• The e2e tests will be delivered in separate PR because the other PR that adds e2e tests hasn't been merged yet.

I have verified this PR works in these browsers (latest versions):

• Chrome
• Firefox
• Safari (macOS)
• Safari (iOS) [I don't have a device, I need help testing in iPhone]
• Chrome for Android
• Not applicable

What else has been done to verify that this works as intended?

• Test plan

Test evidence:

Date Notes

Note values:

• <date_note>2025-12-21T23:30:05</date_note>
• <date_note>2025-12-21</date_note>

Why is this the best possible solution? Were any other approaches considered?

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

• Datetimes with a timezone offset will result in a null / empty string. We need user research to determine if it should honor the timezone (in local time, it could be one date back or forward) or truncate to the date part (yyyy-mm-dd) as Enketo does.

Do we need any specific form for testing your changes? If so, please attach one.

I need help testing on iPhone devices.
A test plan is in the ticket, and the test evidence is in the previous section.

What's changed

• The @js-temporal/polyfill library was replaced with temporal-polyfill
• Date constant file was relocated from the 'packages/xpath' to packages/common/src/constants/datetime.ts
• A new demo form for dates was added, and also the date note was added to the note's demo form
• New validation was added to packages/xpath/src/lib/datetime/coercion.ts to prevent out-of-range offsets
  • Webkit (Safari) parses invalid offsets like "-24:00" while Chrome and Firefox reject them. Using Temporal.TimeZone.from ensures consistent rejection of out-of-spec offsets across browsers, aligning with the Temporal spec’s max of ±23:59.
• Adds a new Vue component for the Input Date and adds support for date notes.
• Adds a new Date encode and encode that interprets date like or datetime like without timezone offset, to date only (yyyy-mm-dd).
• Adds Z-index Layer System with documentation
  • Error banner doesn't overlap the calendar
  • Feedback button doesn't overlap the dialog

Note: Calendar's translation is to be resolved in this ticket: #332