fix: simplify date range picker to Airbnb-style selection (calcom#25386)

* feat: simplify date range picker to Airbnb-style selection

Co-Authored-By: eunjae@cal.com <hey@eunjae.dev>

* feat: apply Airbnb-style selection to allowPastDates branch

Co-Authored-By: eunjae@cal.com <hey@eunjae.dev>

* refactor: extract date range selection logic and add unit tests

- Extract date range selection logic into pure function (dateRangeLogic.ts)
- Remove unused allowPastDates parameter from selection logic
- Add comprehensive unit tests (11 test cases covering all scenarios)
- Simplify DateRangePicker component (30+ lines -> 5 lines)
- Improve separation of concerns: allowPastDates only controls calendar date restrictions

* style update

* feat: add hover highlighting for date range selection

When a start date is selected and user hovers over other dates,
the potential range between start and hovered date now shows
bg-emphasis background for better visual feedback.

Co-Authored-By: eunjae@cal.com <hey@eunjae.dev>

* memoize hovering range and update styles

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Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: eunjae-lee