fix: wrong dates on OOO due to summer time

[eunjae-lee]

What does this PR do?

This PR fixes wrong dates on OOO due to summer time.

• Fixes CAL-4629

Why?

I'm currently in Paris on March 28 2025, and it's GMT+1 and CET (Central European Standard Time).
However, if I choose April 1 2025, that's after the summer time begins, which means GMT+2 and CEST (Central European Summer Time).

We've been using dayjs().utcOffset() which gives me the current offset (60), but we should get offset specifically for the chosen date (120).

Visual Demo (For contributors especially)

This error should no longer happen since this PR ↓

Screenshot.2025-03-28.at.12.01.23.mp4

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• N/A - I have updated the developer docs in /docs if this PR makes changes that would require a documentation change. If N/A, write N/A here and check the checkbox.
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

[linear]

CAL-4629 OOO shows wrong dates

[vercel]

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2 Skipped Deployments

Name	Status	Preview	Comments	Updated (UTC)
cal	⬜️ Ignored (Inspect)	Visit Preview		Mar 28, 2025 2:07pm
calcom-web-canary	⬜️ Ignored (Inspect)	Visit Preview		Mar 28, 2025 2:07pm

[graphite-app]

Graphite Automations

"Add consumer team as reviewer" took an action on this PR • (03/28/25)

1 reviewer was added to this PR based on Keith Williams's automation.

"Add ready-for-e2e label" took an action on this PR • (03/28/25)

1 label was added to this PR based on Keith Williams's automation.

[github-actions]

E2E results are ready!

• Workflow #54468.1 latest results