feat(datetimerangepicker): fix background transparency; allow setting default date tab

[hoorayimhelping]

• When testing DateTimeRangePicker in an app, the background was transparent, which isn't apparent in the storybook. This fixes that.

• This also adds the ability to set the default date tab to startDate or endDate for instances where picked dates will be in the past

• Cleans up some of the common code as well

[changeset-bot]

🦋 Changeset detected

Latest commit: 81e330e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@clickhouse/click-ui	Minor

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[github-actions]

Claude finished @hoorayimhelping's task in 1m 8s —— View job

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All previously flagged items are resolved. This PR is clean and ready to merge.

✅ Background fix — CalendarRendererContainer correctly uses theme.click.datePicker.dateOption.color.background.default. No hardcoded colors anywhere in the changed files.

✅ defaultActiveTab feature — TabbedCalendar correctly initializes activeTab from defaultActiveTab via useState and syncs dynamic prop changes via useEffect (lines 593–597). Tab type is both exported from DateTimeRangePicker.tsx (line 566) and re-exported through index.ts (line 7) — consumers can import it directly.

✅ Test fixes — The misleading test name is now "preserves user-selected tab when defaultActiveTab is re-rendered with the same value" (line 568), and the typo 'setting a default acttive tab' is corrected to 'setting a default active tab' (line 399). Coverage spans initial state, behavioral interaction, and dynamic re-render scenarios.

✅ Common.tsx refactor — Clean extraction with no breaking changes to consumers.

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💡 Suggestion (non-blocking)

• Changeset description (.changeset/wet-monkeys-ring.md): Per CONVENTIONS.md, minor feature changesets benefit from a short usage snippet. Worth adding:

  Adds the ability to set a default date tab between startDate and endDate (defaults to startDate)
  
  Usage:
  ```tsx
  <DateTimeRangePicker defaultActiveTab="endDate" onSelectDateRange={...} />

✅ Ready to merge.

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