feat: Migrate Anonymous Projects on Signup

[iamanishsrivastava]

🚀 Feature Request

Allow projects linked to an anonymousUserId to be re-linked to a userId once a user signs up.

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🎯 Motivation

So anonymous users don’t lose their work after registration.

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🧩 Solution or Approach

• Endpoint accepts userId + anonymousUserId
• Updates all associated projects to new user

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✅ Acceptance Criteria

• Backend endpoint updates project ownership
• AnonymousUser entry may optionally be deleted

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📎 Additional Context

This finalizes the anonymous-to-auth flow.

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🔀 Related Branch

feat/anon-data-migration

[github-actions]

This GitHub issue proposes a feature to enable the migration of projects associated with an anonymousUserId to a registered userId when a user signs up, ensuring users retain their work after registration. The solution involves a backend endpoint that accepts both userId and anonymousUserId, updating the ownership of all related projects, with an optional deletion of the AnonymousUser entry. The feature is part of finalizing the anonymous-to-authenticated user workflow and is being developed on the feat/anon-data-migration branch. Key acceptance criteria include ensuring the project ownership update is handled correctly via the endpoint.