fix: pass booking date to getUTCOffsetByTimezone to handle DST correctly

[neilspaul]

What does this PR do?

Fixes a DST timezone offset bug where getUTCOffsetByTimezone() was called without a date, causing it to use the current moment's UTC offset instead of the booking date's offset.

For DST-observing timezones (e.g. America/Los_Angeles), the UTC offset differs between PST (-480 min) and PDT (-420 min). When the booking date falls in a different DST period than "now", the wrong offset was fed into calculatePeriodLimits and isOutOfBounds, shifting period boundaries and causing bookings to appear at incorrect times for cross-timezone users (e.g. PDT booker → IST host).

What changed?

• validateBookingTimeIsNotOutOfBounds.ts: Pass reqBodyStartTime (already available as a parameter) to getUTCOffsetByTimezone so the offset matches the booking date, not the current date
• slots/util.ts: Pass input.startTime to getUTCOffsetByTimezone so slot period limits use the correct DST offset

Both are 2-line changes. The getUTCOffsetByTimezone function already accepts an optional date parameter — it just wasn't being used at these call sites.

How to test

1. Set host timezone to Asia/Kolkata (IST)
2. Set booker timezone to America/Los_Angeles
3. Book a slot in July (PDT) — verify the time shows correctly in IST
4. Book a slot in January (PST) — verify the time shows correctly in IST
5. Run unit tests:

   TZ=UTC yarn vitest run packages/lib/dayjs/getUTCOffsetByTimezone.test.ts
   TZ=UTC yarn vitest run packages/features/bookings/lib/handleNewBooking/validateBookingTimeIsNotOutOfBounds.test.ts

Type of change

• Bug fix (non-breaking change which fixes an issue)

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent PR review)
• I have updated the developer docs (if relevant)
• I have added tests to cover my changes (if relevant)
• I have run the relevant tests and they pass

Made with Cursor

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