front/e2e: Simplifier les page modals et regrouper les locators

[Maymanaf]

Description and goal

Topic 1:
The current modals, such as STDCM, have grown too large, with some exceeding 800 lines of code. This makes them difficult to understand and maintain. These modals need to be split into simplified versions to improve readability and modularity.

Topic 2:
Page models with large numbers of locators can be challenging to navigate. Locators are currently declared both in the class and the constructor, leading to redundancy. This process should be optimized so that locators are declared only once.

Acceptance criteria

• Improve code readability maintainability