Create opening frontend

[craigyu]

Description

Implement the frontend flow for creating an opening.

The feature should provide a create opening form, validate required fields before submission, submit the opening creation request to the backend, and handle success and error states clearly.

Scope

• Build the create opening form UI.
• Add client-side validation for required opening fields.
• Connect the form to the opening creation API.
• Handle successful submission.
• Handle submission errors.
• Prevent duplicate submissions while a request is in progress.

Acceptance Criteria

• Create opening form is available in the frontend.
• Required fields are validated before submission.
• Users receive clear validation feedback for missing or invalid fields.
• Valid form data is submitted to the backend.
• Successful submission shows a success state and/or navigates the user appropriately.
• Failed submission shows an error state with a useful message.
• Submit action is disabled or protected while submission is in progress.