fix: Add validation and consistent data structure for survey 'Other' options

[viva-jinyi]

Summary

• Added validation to prevent users from proceeding when "Other" is selected but text input is empty
• Changed data structure to send consistent string values to database instead of mixed objects
• Both useCase and industry now send user input directly when "Other" is selected

Changes

• Added useCaseOther field and input to survey form
• Updated validStep2 to validate useCaseOther when useCase is 'other'
• Modified submit payload to send string values consistently for both useCase and industry fields

Test plan

• Select "Other" for use case without filling input → Next button disabled
• Select "Other" for industry without filling input → Next button disabled
• Fill in "Other" text inputs → Next button enabled
• Submit survey with "Other" selections → Payload sends user input as string values

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[github-actions]

🎭 Playwright Test Results

❌ Some tests failed!

⏰ Completed at: 09/17/2025, 10:49:59 AM UTC

📊 Test Reports by Browser

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• ❌ mobile-chrome: View Report

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⚠️ Please check the test reports for details on failures.

[DrJKL]

Can they only pick one use case?
If it ends up being multiselect this logic will probably need to change.

[DrJKL]

#5625
Once this goes in, the placeholder will be flagged as something to translate.