Features branch

[barrera77]

1. Added CreatePost endpoint in the PostsController:

• [HttpPost] public ActionResult CreatePost([FromBody] PostDto postDto)
• This receives the post JSON, validates it, calls the service to create it, and returns 201 Created with the new slug.

2. Implemented CreatePost in PostService:

• Maps the incoming PostDto to a Post entity.
• Generates a new GUID automatically for Id if none is provided.
• Sets CreatedDate if not provided.
• Adds the post to the database and calls _context.SaveChanges().
• Converts the saved entity back to PostDto and returns it.