fix(chore): Reduce combobox and date-picker re-render

[karim-semmoud]

Summary

Reduces DOM churn in combobox and date-picker re-renders. Both components subscribe to Zag machine updates and call render() on every state change; previously they tore down and rebuilt large parts of the list/calendar on each pass.

Changes

assets/components/combobox.ts

• Replaced full list teardown (remove() all items/groups, re-clone from templates) with incremental sync:
  • Flat lists: reuse existing items by data-value, clone only missing ones, reorder with insertBefore, drop filtered-out items
  • Grouped lists: reuse group shells and nested items the same way
  • Empty state: show/hide empty part without touching unrelated DOM when possible
• Fixed grouped mode cleanup: only direct list-level items are removed before sync (nested group items were incorrectly wiped every render via querySelectorAll)

assets/components/date-picker.ts

• Day/month/year calendar tables now reuse <tr>/<td> nodes instead of tbody.innerHTML = ""
• Cells keyed with data-date-cell (day: YYYY-M-D, month: {year}-{month}, year: {year})
• Updates Zag props and text in place; creates nodes only when structure changes
• Day table header row is reused when weekday column count is unchanged

Tests

• assets/test/component/combobox.test.ts: flat reuse, filter removal, grouped reuse
• assets/test/component/date-picker.test.ts: day cell and header reuse on repeated render

Why

On every LiveView patch or Zag state update (filter, open, select, navigate month), the old code destroyed and recreated every list item or calendar cell. That added layout cost, broke focus/hover stability, and scaled poorly with large option lists or open calendars.