Add goal icon picker support

[Hr-cd]

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[Hr-cd]

Add goal icon picker support

[Hr-cd]

Summary

This pull request adds support for goal icons throughout the application.

Backend Changes

• Added an optional Icon field to the Goal model.
• Updated the backend to support storing and returning goal icons.
• Added unit test coverage for the GetGoalsForUser endpoint.

Frontend Changes

• Updated the client Goal model to include the icon property.
• Displayed goal icons on goal cards.
• Integrated an emoji picker to allow users to add and change icons.
• Updated GoalManager to persist icon changes.

Networking

• Added a PUT request for updating goals.
• Connected the frontend and backend so icon changes persist after refresh.

Testing

• Verified that goal icons are correctly saved and returned by the API.
• Added automated test coverage for GetGoalsForUser.