fix(date-field): open DatePicker calendar on the typed/selected date

[interacsean]

Summary

Typing a date into an empty DatePicker and pressing Alt+↓ opened the calendar on today's month, so →+Enter picked tomorrow instead of 21 Dec.

useCalendarState sets the calendar's focused date once, at mount (use-calendar-base-state.ts), and nothing updated it from the field value afterwards. The calendar state also persists while the popover is closed, so reopening landed on today's month or on whatever month was last viewed. The APG date-picker dialog and react-aria instead open on the selected or typed date, falling back to today.

Changes

• DatePicker: a new handleOpenChange moves the calendar to the current value, or today, on every open. It covers both the trigger click and Alt+↓. The date still goes through setFocusedDate, so it stays within minValue/maxValue.
• DateRangePicker: it already moved to the start date on open, but only when one was set. It now falls back to a typed end date, then today, instead of a stale last-viewed month.
• Regression tests: the typed-date + Alt+↓ + →/Enter repro; a controlled value changed while closed, then cleared; and a range with only the end date set. All three fail without the fix.
• Patch changeset.

Verification

Local: fmt, lint, type-check, the full test suite (1827 core tests) and docs:check all pass. I haven't checked it by hand in the vite showcase; the regression tests replay the repro steps.

Closes tailor-inc/platform-planning#2001

🤖 Generated with Claude Code

[github-actions]

Code Metrics Report

	main (bad3569)	#574 (657df5f)	+/-
Coverage	87.5%	87.6%	+0.0%
Test Execution Time	1m25s	1m49s	+24s

Details

  |                     | main (bad3569) | #574 (657df5f) |  +/-  |
  |---------------------|----------------|----------------|-------|
+ | Coverage            |          87.5% |          87.6% | +0.0% |
  |   Files             |            206 |            206 |     0 |
  |   Lines             |           6084 |           6089 |    +5 |
+ |   Covered           |           5325 |           5334 |    +9 |
- | Test Execution Time |          1m25s |          1m49s |  +24s |

Code coverage of files in pull request scope (94.8% → 96.5%, patch 100.0%)

Files	Coverage	+/-	Patch Coverage	Status
packages/core/src/components/calendar/use-calendar-base-state.ts	93.3%	+3.7%	-	affected
packages/core/src/components/date-field/date-field.tsx	100.0%	0.0%	100.0%	modified
packages/core/src/components/date-field/date-range-picker.tsx	97.7%	+0.0%	100.0%	modified

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Reported by octocov