fix: include templateId in the basicInfo object during form submission

[Kariamos]

resolves UN-1697

[sentry]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: src/pages/JoinPage/useJoinSubmit.tsx

Function	Unhandled Issue
useJoinSubmit	TypeError: useSearchParams(...).get is not a function ... Event Count: 1 Affected Users: 1

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[Copilot]

Pull Request Overview

This PR fixes a bug where the templateId parameter from URL search parameters was not being included in the form submission data. The fix parses the template parameter from the URL, validates it as an integer, and conditionally includes it in the basicInfo object during join form submission.

• Added URL parameter parsing for the 'template' query parameter
• Implemented validation to ensure template parameter is a valid integer
• Included templateId in the basicInfo object when submitting the form

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