Feature/backend put update

[janhvi1623]

This PR adds and finalizes the Goal management backend API.

Changes included:

• Implemented GET endpoints for retrieving goals
• Implemented POST endpoint to create new goals
• Implemented PUT endpoint to update existing goals
• Implemented DELETE endpoint to remove goals
• Integrated user-goal linking logic in POST request
• Added unit tests for GoalController to verify API behavior

All endpoints are working with service layer integration and test coverage.

[gitguardian]

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GitGuardian id	GitGuardian status	Secret	Commit	Filename
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