fix: preserve array query params in redirect URL serialization

[Akash504-ai]

What does this PR do?

Fixes incorrect serialization of query parameters containing array values in redirect logic.

Previously, context.query was cast to Record<string, string> and passed to URLSearchParams, which caused array query params to be flattened (e.g. user=john,doe instead of user=john&user=doe).

This PR ensures query params are properly preserved by handling both string and string[] values.

• Fixes Incorrect serialization of array query parameters in redirect logic #28687

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How should this be tested?

1. Open a URL with repeated query params: /john+doe?user=john&user=doe

2. Trigger a redirect (dynamic group or single event).

3. Verify the redirected URL:

• Before fix: user=john,doe
• After fix: user=john&user=doe

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Mandatory Tasks

• I have self-reviewed the code
• I have updated the developer docs if required (N/A)
• I confirm tests are not required for this small fix

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Checklist

• My PR is small and focused (1 file change)
• Code follows existing style

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[CLAassistant]

All committers have signed the CLA.

[cubic-dev-ai]

No issues found across 1 file

[Akash504-ai]

All checks look good except PR Update / required ( it seems unrelated to this change). Ready for review.

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.

[sahitya-chandra]

this is dead code now, we can remove this import { encode } from "node:querystring";

[sahitya-chandra]

PR looks fine, but can you still add a before and after video of changes

[Akash504-ai]

Before:
Query params with array values were flattened: user=john%2Cdoe

After:
Query params are preserved correctly: user=john&user=doe

Example.Domain.-.Brave.2026-04-01.15-50-40.mp4

[Akash504-ai]

Ready for review. All feedback addressed and branch updated.

[sahitya-chandra]

a video of issue being reproduced on locally running cal.com, not on example.com

[Akash504-ai]

Hi, I tried setting up cal.com locally to reproduce the issue, but I am running into persistent environment/database setup issues (Prisma/Postgres access errors) that seem unrelated to the PR. I have demonstrated the exact root cause and fix using URLSearchParams behavior (array serialization vs append), which is the underlying issue this PR addresses.

Would that be sufficient, or is there a specific minimal setup or route I should use in the app to reproduce this without full local setup?