feat: add 40-minute duration option for multiple duration event types

[devin-ai-integration]

What does this PR do?

Adds 40 minutes as an available duration option when configuring multiple duration options for event types. Previously, the available durations jumped from 30 to 45 minutes, skipping 40 minutes which is a commonly requested duration.

Changes:

• Added 40 to the multipleDurationOptions array in EventSetupTab.tsx
• Added comprehensive unit tests for 40-minute slot generation

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• I confirm automated tests are in place that prove my fix is effective or that my feature works.
• I have updated the developer docs in /docs if this PR makes changes that would require a documentation change. N/A - no documentation changes needed.

How should this be tested?

1. Go to Event Types → Edit an event type → Setup tab
2. Enable "Allow booker to select duration"
3. Click the "Available durations" dropdown
4. Verify that 40 minutes is now available as an option (between 30 and 45 minutes)
5. Select 40 minutes and save
6. Verify the booking page shows 40 minutes as a selectable duration

Unit tests added:

• TZ=UTC yarn test packages/features/schedules/lib/slots.test.ts -t "40-minute" - runs 5 tests covering:
  • Full day slot generation (36 slots in 24 hours)
  • Correct 40-minute time intervals (9:00, 9:40, 10:20)
  • Default duration handling for variable length events
  • Same-day booking with time constraints
  • Multiple date ranges

Checklist

• My code follows the style guidelines of this project
• I have checked if my changes generate no new warnings

---

Link to Devin run: https://app.devin.ai/sessions/a584b7947d0844cfb584b008544f6ded
Requested by: ali@cal.com

Note for reviewers: The diff includes some auto-formatting changes from biome lint (import reordering, CSS class sorting). The core change is simply adding 40 to the duration options array on line 78.

[devin-ai-integration]

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[cubic-dev-ai]

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