Support icons

[fortune-c]

1. Modified Goal model to include an optional Icon string field.
2. Updated the database seeding to include icons for existing goals.
3. Added a PUT endpoint to update the Icon for a goal.
4. Verified that API responses include icons when present.
5. Verified using Postman that emoji changes persist after refresh.
6. Added unit tests for the GetGoalsForUser endpoint to ensure coverage.

[gitguardian]

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