[FEATURE] Add JWT authorization requirement to all relevant backend endpoints

## Feature Description

For each new /api/v1 endpoint that should require authentication, add the decorator(s) to enforce those policies.

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## Acceptance Criteria & Solution Requirements
*To close this issue, the following must be met (can be finalized in the comments):*
- [ ] 1. Application runs as expected with the new feature integrated seamlessly.
- [ ] 2. Code quality metrics are maintained, and linting has been considered in development.
- [ ] 3. Testing metrics are maintained, and tests have been updated/added wherever relevant during development.
- [ ] 4. Documentation has been updated to reflect the changes made during development.
- [ ] 5. All endpoints have been considered for login requirement.
- [ ] 6. A new decorator has been added that requires that the logged-in user is also an admin. Use an `is_admin` boolean JWT key.
- [ ] 7. All endpoints have been considered for admin requirement.

Find the backend API endpoints in the codebase, likely in a directory like 'api/v1/'. Identify which endpoints need JWT authentication and admin checks. Look for existing decorators for authentication. The new admin decorator should check for an 'is_admin' boolean in the JWT. Update tests to verify protected endpoints reject unauthorized requests and that admin endpoints require the admin flag.

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