Implement Workout Session API Client Functions

[Lance-Yuriel]

Is your feature request related to a problem? Please describe.
I'm trying to contribute to this project and noticed that the workout session API client functions in src/shared/lib/workout-session/workout-session.api.ts are incomplete. They currently just return empty arrays or placeholder values instead of making actual requests to the server.

Describe the solution you'd like
I'd like to implement the actual HTTP requests for these four functions:

• getAll() - Get all workout sessions from the server
• create() - Create a new workout session
• update() - Update an existing workout session
• complete() - Mark a workout session as completed

I want to use the standard fetch API to make these requests to the existing API endpoints.

Describe alternatives you've considered
I'm not sure what other approaches would work here, but I think using fetch is the right choice since it's built into JavaScript.

Additional context
I can see the server-side API endpoints already exist, so I just need to implement the client-side code that calls them.